A thru C | D thru O (This page below) | P thru Z

Defibrillation - The use of an electrical device (defibrillator) to give an electric shock to the heart to help restore a normal heartbeat. It is used for dangerous arrhythmias, such as ventricular tachycardia or ventricular fibrillation, and in cardiac arrest.

Defibrillator - A device that delivers "pacing" or an electric shock to the heart when an abnormal rhythm (arrhythmia) is detected. A defibrillator may be external or internal. External defibrillators use pads that are placed on the chest to deliver the electric shock. Internal defibrillators (implantable cardioverter defibrillators or ICDs) look similar to a pacemaker, but they continuously monitor the heart rhythm to detect overly rapid arrhythmias such as ventricular tachycardia or ventricular fibrillation. The ICD corrects the heart rhythm by delivering precisely calibrated and timed electrical shocks to restore a normal heartbeat when one of these dangerous arrhythmias has occurred.

Diabetes (Diabetes Mellitus) - Insulin is a hormone produced in the pancreas, an organ near the stomach. Insulin is needed to turn sugar and other food into energy. With diabetes, the body either doesn't make enough insulin or can't use its own insulin as well as it should, or both. This causes sugars to build up too high in the blood. Type 2 diabetes is the most common form. It appears most often in middle-aged adults; however, adolescents and young adults are developing type 2 diabetes at an alarming rate. Type 1 diabetes usually occurs in children and young adults. In type 1, the pancreas makes little or no insulin. Without daily injections of insulin, people with type 1 diabetes won't survive. Untreated diabetes can lead to many serious medical problems. These include blindness, kidney disease, nerve disease, limb amputations and cardiovascular disease.

Diastolic Blood Pressure - The lowest blood pressure measured in the arteries that occurs when the heart muscle relaxes between beats. In a typical blood pressure reading, such as 120/78, the lower number is diastolic blood pressure. It is measured in millimeters of mercury (mmHg).

Diastolic Dysfunction - Abnormal function of the heart during its relaxation phase (diastole). While the heart's ability to contract and pump blood may be maintained, its ability to relax and fill is compromised. Filling of the heart's lower chambers (ventricles) is impaired because the chamber is stiff (non-compliant), due to thickening (hypertrophy) or cardiomyopathy. It may also be due to stiffening of the sac around the heart (pericardium). Though the ability to contract may be preserved, diastolic pressure is elevated and cardiac output reduced.

Diastolic Heart Failure - A condition in which the pumping chambers (ventricles) of the heart become thickened, grow stiff and cannot relax enough to adequately fill the heart's lower chambers (ventricles) with blood. The fluid then backs up into organs and causes swelling (edema) (especially in feet and ankles) and congestion even though the heart's pumping function (ejection fraction) is normal. This type of heart failure is caused by conditions such as acute ischemia, systolic hypertension with enlargement of the left ventricular muscle, restrictive cardiomyopathy and hypertrophic cardiomyopathy.

Digital Cardiac Angiography (DCA), Digital Subtraction Angiography (DSA) - A modified form of computer imaging that records pictures of the major blood vessels to the heart or brain. It shows blockages, how severe they are and what can be done about them.

Digitalis (also Digoxin, Digitoxin) - A drug that strengthens the contraction of the heart muscle, slows the heart rate and helps eliminate fluid from body tissues. It's often used to treat congestive heart failure and is also used to treat certain heart rhythm abnormalities (arrhythmias).

Diuretic (or Water Pill) - A drug that increases the rate at which urine forms by promoting the excretion of water and salts. This helps to relieve the heart's workload and also decreases the buildup of fluid in the lungs and other parts of the body, such as the ankles and legs. Different diuretics remove fluid at varied rates and through different methods. They are used to treat high blood pressure, congestive heart failure and some congenital heart defects.

Doppler Ultrasound - A test that uses high-frequency sound waves to detect blockages in an artery and to evaluate blood flow.

Drug Interaction - A change in the effect of a drug when taken with a certain other drug, a supplement or food. Its effect may increase or decrease, or a side effect may occur.

Dysarthria - Speech that is slowed, slurred or distorted due to muscular problems caused by damage to the brain or nervous system.

Dysphagia - Difficulty chewing and swallowing food that occurs when one side of the mouth is weak due to stroke or other brain injury. One or both sides of the mouth can lack feeling, increasing the risk of choking.

Dyspnea - Difficult or labored breathing, often caused by heart conditions. Two types of dyspnea are significant in cardiac illness. Dyspnea on exertion (DOE) is the shortness of breath that occurs with increasing activity. Paroxysmal nocturnal dyspnea (PND) is a shortness of breath that awakens a person at night from sleep. Both are significant symptoms in cardiac disease.

Dysrhythmia - (See Arrhythmia)

Ebstein's Anomaly (Ebstein's Malformation) - A congenital heart defect in which the tricuspid valve is abnormally formed. The tricuspid valve is one of the heart's four valves. It normally swings open to allow the smooth passage of blood from the right atrium to the right ventricle, and then closes. Blood should flow in one direction and only at the right time. The tricuspid valve normally has three "flaps" or leaflets. In Ebstein's anomaly, one or two of the three flaps are stuck to the wall of the heart and don't move normally. Often there's also a hole in the wall between the atria, the heart's two upper chambers. This hole is called an atrial septal defect or ASD. Since the valve doesn't work properly, it may leak. Ebstein's anomaly is mild in most adults who have it, so they don't need surgery. However sometimes the tricuspid valve leaks severely enough to result in heart failure or cyanosis. Then surgery may be required.

Echocardiography (or Echocardiogram) - A diagnostic method in which a hand-held device is placed on the chest and high-frequency sound waves (ultrasound) are used to produce images of the heart's size, structure and motion. An "echo" provides valuable information about the health of the heart and helps gather information about abnormal rhythms (arrhythmias).

Edema - Swelling due to an abnormally large amount of fluid in the intracellular body tissue spaces. Edema is common in the legs, ankles and lungs of people with heart failure.

Eisenmenger's Complex - A ventricular septal congenital heart defect coupled with pulmonary high blood pressure, the passage of blood from the right side of the heart to the left (right to left shunt), an enlarged right ventricle and a latent or clearly visible bluish discoloration of the skin (cyanosis). It may also include a malpositioned aorta that receives ejected blood from both the right and left ventricles (an overriding aorta). People with Eisenmenger's complex, before and after treatment, are at risk for getting an infection within the aorta or the heart valves (endocarditis). To help prevent this, they'll need to take antibiotics before certain dental and surgical procedures.

Ejection Fraction - During each heartbeat, the heart contracts and relaxes. The ventricles (the heart's lower chambers) are the pumping chambers. In contraction (systole), the heart ejects blood from the ventricles. When the heart relaxes (diastole), the ventricles fill with blood. The heart never empties all of the blood from the ventricles, no matter how hard it beats. The ejection fraction is the percentage of blood that is pumped out with each heartbeat. This measures the heart's capacity and functioning ability. Ejection fraction is usually measured in the left ventricle because it is the heart's main pumping chamber. A normal ejection fraction in a person at rest is typically between 55 and 70 percent. If the heart muscle has been damaged by heart attack, heart muscle disease or heart valve problems, the ejection fraction may be below normal.

Electrocardiogram (or Electrocardiography, ECG or EKG) - A quick, painless test that records the electrical activity of the heart. It may be taken at rest or during exercise. It is the standard clinical tool for diagnosing arrhythmias (abnormal rhythms) and to check if the heart is getting enough blood or if areas of the heart are abnormally thick. Small patches called electrodes are placed on different parts of the body. Different tracings of the heart's electrical activity can be made and permanently recorded on paper or in a computer. Three major waves of electric signals appear on the ECG. Each one shows a different part of the heartbeat. The P wave records the electrical activity of the atria. The QRS wave records the electrical activity of the ventricles, and the T wave records the heart's return to the resting state. Doctors study the shape and size of the waves, the time between waves and the rate and regularity of beating. This tells a lot about the heart and its rhythm.

Electroencephalogram (EEG) - A graphic record of the electrical impulses produced by the brain.

Electron-Beam Computed Tomography (EBCT or Ultrafast®CT) - The high-speed form of X-ray imaging technology. It's used to evaluate various structures and functions in the heart and to measure calcium deposits in the coronary arteries. Electrophysiologic Testing - A procedure used to provoke known but infrequent arrhythmias and to unmask suspected arrhythmias. Using local anesthesia, temporary electrode catheters are positioned in the heart's atria and/or ventricles and at strategic locations along the conduction system. They record cardiac electrical signals and "map" the spread of electrical impulses during each heartbeat.

Embolus - A blood clot or other particle that forms in one part of the body, then moves through the bloodstream until it lodges in a narrowed vessel and blocks the flow of blood (circulation).

Emotional Lability - An effect of stroke in which a survivor cries or laughs or has sudden mood swings for no apparent reason. Endarterectomy - Surgical removal of plaque deposits or blood clots in an artery.

Endocarditis - An inflammation of the heart lining or valves, usually caused by bacterial infection. People with prosthetic heart valves, abnormal heart valves, a history of endocarditis or congenital heart defects are at increased risk of this disease. Endocarditis can also be caused by injection drug use and recent dental surgery.

Endomyocardial Biopsy - (See Myocardial Biopsy)

Endothelium - The smooth inner lining of some body structures, including the heart (endocardium) and blood vessels.

Enzyme - A complex chemical that can speed up specific biochemical processes in the body.

Estrogen - A hormone produced in a woman's body. Synthetic forms of estrogen are used in oral contraceptives and hormone replacement therapy.

Exercise Stress Test (Treadmill Test) - A diagnostic test in which a person walks on a treadmill or pedals a stationary bicycle while hooked up to equipment that monitors the heart. The test monitors heart rate, breathing, blood pressure, electrical activity (on an electrocardiogram) and the person's level of tiredness. It shows if the heart's blood supply is sufficient and if the heart rhythm is normal. (Also known as Exercise Test, Exercise Cardiac Stress Test or ECST.)

Fellow - A licensed physician who's completed medical school (four years) and specialty training (three-seven years) in pediatrics, medicine, surgery, anesthesiology, etc. and is eligible for board certification in that specialty. Subspecialty training then takes place (for example, in cardiothoracic surgery, pediatric cardiology) during which time the physician is called a "fellow."

Fibrillation - Fast, uncoordinated contractions of individual heart muscle fibers. The heart chamber involved can't contract all at once and pumps blood ineffectively, if at all.

HDL Cholesterol (High-Density Lipoprotein Cholesterol) - Often called "good" cholesterol because a high level of it seems to protect against heart attack and other cardiovascular conditions. People with a low HDL cholesterol level (less than 40 mg/dL in men, less than 50 mg/dL in women) have a higher risk of heart disease. A low level of HDL cholesterol also may raise stroke risk.

Heart Attack (Myocardial Infarction) - Death of or damage to part of the heart muscle due to an insufficient blood supply. Heart attacks occur when one of the coronary arteries that supply blood to the heart muscle is blocked. Blockage is usually caused from a buildup of plaque (deposits of fat-like substances) due to atherosclerosis. If a plaque deposit tears or ruptures, a blood clot may form and block the artery, causing a heart attack. Heart attack is also called a coronary thrombosis or coronary occlusion.

Heart Block (or AV Block) - The heart's "natural" pacemaker is called the sinoatrial (SA) node or sinus node and is located in the right atrium. It produces electrical impulses that make the heart beat. For the heart to beat properly, the signal must travel from the SA node down a specific path to reach the ventricles (pumping chambers of the heart). As the signal goes from the atria to the ventricles, it passes through specialized conducting tissue called the atrioventricular (AV) node. Sometimes the electrical signal from the heart's upper to lower chambers is impaired or doesn't transmit. This may occur in the conduction pathway or in the AV node. This is "heart block" or "AV block." Heart block is classified according to the level of impairment - first-degree heart block, second-degree heart block or third-degree (complete) heart block.

Heart Disease, Ischemic - The most common form of heart disease, in which narrowed or blocked coronary arteries result in decreased blood supply (ischemia).

Heart Failure (Congestive Heart Failure) - The inability of the heart to pump enough blood to meet the needs of the body's other organs. This can cause fluid to build up in the body, which is seen as swelling (edema), most commonly in the lower legs and ankles. Heart failure (HF) also reduces the kidneys' ability to dispose of sodium and water, making edema worse. Fluid can also collect in the lungs and interfere with breathing, causing shortness of breath. HF is almost always a chronic, long-term condition, although it can sometimes develop suddenly. It may affect the right side, the left side, or both sides of the heart. Right-sided HF affects the gastrointestinal tract and the extremities. Right-sided HF usually occurs as a result of left-sided HF. Left-sided HF affects the lungs, but as the heart's ability to pump decreases, fluid builds up in tissues throughout the body. Most areas of the body can be affected when both sides of the heart fail. In HF, the failing heart keeps working, but inefficiently. The most common causes of HF are coronary artery disease (CAD), previous heart attack and hypertension (high blood pressure). Other causes of heart failure include valvular heart disease, congenital heart disease, dilated cardiomyopathy, endocarditis or myocarditis, lung disease and heart tumor. HF becomes more common with advancing age. You are also at increased risk for developing HF if you are overweight, have diabetes, smoke cigarettes, abuse alcohol or use cocaine.

Heart Murmur - An abnormal sound in the heart caused by defective heart valves or holes in the heart walls. The sound is made by blood circulating through the heart's chambers and valves, or through blood vessels near the heart. A person can be born with a heart murmur or it can be caused by pregnancy, fever, thyrotoxicosis (a condition resulting from an overactive thyroid gland) or anemia.

Heart Rate - The heart contracts (beats) as the electrical impulse moves through it. This normally occurs 60 to 100 times a minute. The heart's upper chambers (atria) contract a split-second before the lower chambers (ventricles). This lets the atria empty their blood into the ventricles before the ventricles contract.

Heart Transplant - Surgery that replaces a damaged heart with a healthy heart taken from a donor who has been declared brain dead.

Heart Valve - There are four valves in the heart. The valves control the direction of blood flow through the heart by opening and closing with each heartbeat. The valves permit the blood to flow in only one direction. The four valves are: tricuspid valve (between the right atrium and the right ventricle); pulmonary valve (between the right ventricle and the pulmonary artery; mitral valve (between the left atrium and the left ventricle) and aortic valve (between the left ventricle and the aorta).

Heart Valve Replacement Surgery (Artificial Heart Valve Surgery) - Open-heart surgery to replace a defective or diseased heart valve. Replacement heart valves are either natural (biologic) or artificial (mechanical). Natural valves are from human donors. Modified natural valves come from animal donors. Artificial valves are made of metal.

Hemorrhage - Severe bleeding leading to excessive blood loss.

Hemorrhagic Stroke (Brain Hemorrhage) - Cerebral hemorrhage occurs when a blood vessel or an aneurysm bursts in the brain, causing bleeding inside the brain. Subarachnoid hemorrhages occur when a blood vessel on the brain's surface ruptures and bleeds into the space between the brain and the skull. The brain is very sensitive to bleeding, and damage can occur very rapidly. This may be due to the presence of the blood itself or due to the pressure on the brain caused by the fluid. Hemorrhagic stroke can also be caused by a head injury or a burst aneurysm. An aneurysm is a weak spot in an artery wall, which balloons out because of the pressure of the blood circulating inside the affected artery. Eventually, it can burst and cause serious harm. The larger the aneurysm is, the more likely it is to burst. It is unclear why people develop aneurysms, but genes may play a role, since aneurysms run in families.

Heredity - The passing of a genetic quality or trait from parent to offspring.

High Blood Pressure (Hypertension) - A chronic increase in blood pressure above normal range. Blood pressure is the pressure of the blood against the walls of the arteries. Optimal blood pressure is less than 120/80 mm Hg. High blood pressure, or hypertension, is a condition in which blood pressure levels are consistently above the normal range. Blood pressures of 120-139/80-89 mm Hg are considered prehypertension. People with pre-hypertension are likely to develop high blood pressure unless steps are taken to control blood pressure. Blood pressure is considered high if it is 140/90 mm Hg or higher. High blood pressure increases the risk for heart attack, angina, stroke, kidney failure and peripheral artery disease (PAD). High blood pressure may also increase the risk of developing fatty deposits in arteries (atherosclerosis). The risk of heart failure also increases due to the increased workload that high blood pressure places on the heart.

High-Density Lipoprotein (HDL) - A type of protein believed to transport cholesterol away from the tissues and to the liver, where it can be removed from the bloodstream. (See HDL Cholesterol)

Holter Monitor - A battery-operated, portable device that measures and tape-records the heart's electrical activity (ECG) continuously for 24 to 48 hours or longer depending on the monitor used. Electrodes (small conducting patches) are placed on the chest and attached to a small recording monitor that is carried in a pocket or in a small pouch worn around the neck. The recording is then analyzed, a report of the heart's activity is tabulated and irregular heart activity is correlated with a diary that is kept of the person's activity at the time. It is very important that symptoms and activities are accurately recorded so that the doctor can correlate them with the Holter monitor findings. (Also called Ambulatory Electrocardiography, Ambulatory ECG or Ambulatory EKG.)

Home-Based Healthcare - In-home care for ongoing medical conditions, usually by visiting nurses. This might include intravenous antibiotics, physical assessment, etc.

Homocysteine - An amino acid naturally found in the blood that may serve as a marker for higher risk of coronary artery disease (CAD), stroke and peripheral vascular disease.

Homograft - Material (usually human heart valves and arteries) donated from a cadaver to be used during complex reconstructive surgery.

Hypercholesterolemia - High levels of blood cholesterol, a major risk factor for coronary heart disease, heart attack and stroke.

Hypertension - Medical term for high blood pressure. (See High Blood Pressure)

Hyperthyroidism - Overactivity of the thyroid gland, leading to overproduction of thyroid hormones. It can make the body's metabolism overactive, leading to symptoms such as weight loss and rapid heart rate.

Hypertriglyceridemia - High levels of triglycerides in the blood. A high triglyceride level combined with low HDL cholesterol or high LDL cholesterol seems to speed up atherosclerosis (fatty buildups of plaque in the arteries). A normal triglyceride level is less than 150 mg/dL.

Hypoplastic Left Heart Syndrome - A congenital defect in which the left side of the heart is underdeveloped - including the aorta, aortic valve, left ventricle and mitral valve. Blood returning from the lungs must flow through an opening in the wall between the atria, called an atrial septal defect. The right ventricle pumps the blood into the pulmonary artery, and blood reaches the aorta through a patent ductus arteriosus. Babies with this syndrome often seem normal at birth, but will come to medical attention within a few days of birth as the ductus closes. They become ashen, have rapid and difficult breathing and have difficulty feeding. It is usually fatal within the first days or months of life without treatment, which can include a heart transplant.

Hypotension - The medical term for abnormally low blood pressure.

Hypothermic Circulatory Arrest - During open-heart surgery, especially in neonates and young children, the body temperature can be lowered to 60-65°F and the heart/lung machine turned off ("circulatory arrest"). This allows the surgeon to most precisely operate on a still (non-beating) heart, in an operative field where cardiac structures can best be seen.

Implantable Cardioverter Defibrillator (ICD) - An internal defibrillator used in patients at risk for recurrent, sustained ventricular tachycardia or fibrillation. ICDs look similar to a pacemaker and are about the size of a pocket watch. They continuously monitor the heart rhythm to detect overly rapid arrhythmias. The ICD corrects the heart rhythm by delivering precisely calibrated and timed electrical shocks to restore a normal heartbeat when one of these dangerous arrhythmias has occurred. ICDs run on batteries and can last many years.

Incidence - The number of new cases of a disease that develop in a population during a one-year period. For some statistics, new and recurrent attacks or cases are combined.

Inferior Vena Cava - A major vein that carries blood from the lower body (legs and abdomen) to the heart.

Intermittent Claudication - Pain, cramping or fatigue in the legs and buttocks that occurs during activity and subsides when a person stands still. It's caused by poor blood circulation in leg arteries due to buildups of plaque. It is a common, early symptom of peripheral artery disease (PAD). This condition may occur in both legs, and the symptoms often get worse over time. Smokers have a much greater risk for this condition. A program of daily walking for short periods, with intermittent stops when pain or cramping occur, may help improve the symptoms, but it is necessary to treat the underlying conditions.

Intern - A term for a physician in first-year training after medical school. The first year of a residency is typically called an internship.

Intraaortic Balloon Pump - A device used in treating severe left ventricular failure. The device essentially assists the left ventricle to pump and increases cardiac output. This helps relieve pulmonary congestion and heart failure.

Intravascular Ultrasound - A technique in which an ultrasound catheter is placed in the bloodstream during a heart catheterization to visualize blood vessels "from the inside." This technique is particularly helpful in cases of complex narrowing (stenosis), as may occur in the aorta (coarctation) or pulmonary arteries.

Invasive Procedure - A medical procedure in which the body is "invaded" or entered by a needle, tube, device or scope. Invasive procedures can include anything from the simple needle prick for a blood test or shot, to inserting a tube, device or scope, to major surgeries.

Ischemia - Reduced blood flow to an organ, usually due to a constricted or blocked artery.

Ischemic Heart Disease (Coronary Artery Disease, Coronary Heart Disease) - Blockages in the coronary arteries lead to ischemia, or decreased blood flow to the heart muscle. Decreased blood flow means decreased oxygen supply to the cells, and the body feels that as pain. When more oxygen is needed, as with exercise, the heart cannot meet the demands. When the heart suffers from a lack of oxygen, chest pain (angina) can occur.

Ischemic Stroke - The death of or injury to brain cells caused when a blood clot or other particle blocks an artery in the brain (cerebral artery) or leading to it, such as the carotid (neck) artery. Cerebral thrombosis and cerebral embolism are ischemic strokes.

J-Curve Phenomenon - When the blood pressure or blood cholesterol levels of large groups of people are plotted on a graph against risk of death from cardiovascular disease (CVD), it often results in a J-shaped curve. This curve shows that those with higher blood pressure and/or cholesterol levels, closer to the top of the curve, are more likely to die from CVD. The curve also shows that those at the lowest end of the curve (with very low blood pressure and/or low cholesterol levels) also have higher CVD mortality. This accounts for the J shape and is known as the J-curve phenomenon. Most evidence, however, indicates that people at the bottom-left part of the curve (with very low blood pressure and low cholesterol levels) tend to be different from the general population in other ways. Those differences may contribute to the apparent increase in mortality.

Kawasaki Disease (Kawasaki Syndrome) - A rare, acute children's illness that involves inflammation of the blood vessels, particularly the coronary arteries, and the heart muscle (myocarditis) or the sac surrounding the heart (pericarditis). It is characterized by fever and swelling and can also cause red eyes, inflammation of the lips and mouth, swollen and red hands and feet, and swollen lymph nodes. The coronary arteries or other parts of the heart are affected in up to 20 percent of children with this disease. The cause has not been determined. (Also known as Mucocutaneous Lymph Node Syndrome.)

Laser Angioplasty - A technique used to open coronary arteries blocked by plaque. A catheter with a laser at its tip is inserted into an artery. Then it's advanced through the artery to the blockage. When the laser is in position, it emits pulsating beams of light that vaporize the plaque.

LDL Cholesterol (Low-Density Lipoprotein) - Often called "bad" cholesterol, LDL cholesterol is the major cholesterol carrier in the blood. If too much LDL cholesterol circulates in the blood, it can slowly build up in the walls of the arteries that lead to the heart and brain. Together with other substances it can form plaque, a thick, hard deposit that can clog those arteries. This condition is known as atherosclerosis. A high level of LDL cholesterol (160 mg/dL and above) reflects an increased risk of heart disease. An optimal level is less than 100 mg/dL. Levels from 100-129 mg/dL are near or optimal. Levels from 130-159 mg/dL are borderline high, which also increases risk for heart disease or stroke. LDL cholesterol level may be a better indicator of risk for a heart attack or stroke than total cholesterol, and drug therapy is initiated based on the level of LDL cholesterol. The lower the LDL cholesterol, the lower the risk for heart disease or stroke. For people with heart disease, the LDL cholesterol should be less than 100 mg/dL. For those with severe heart disease, the doctor may suggest that the LDL cholesterol level be less than 70 mg/dL.

Left-sided Heart Failure (Left-ventricular Heart Failure) - Heart failure in which the left side of the heart must work harder to pump the same amount of blood. This type of heart failure usually causes breathing difficulties.

Left-ventricular Assist Device (LVAD) - A battery-operated mechanical pump that is surgically implanted and is used to aid the natural pumping action of the heart's left ventricle. This device is sometimes called a "bridge to transplant" because it buys time until a heart transplant can be performed.

Lipid - A fatty substance insoluble in blood. Cholesterol, cholesterol compounds, and triglycerides are all lipids. They are transported in the blood as part of large molecules called lipoproteins. Abnormalities in lipids can contribute to heart disease. It is recommended that all adults age 20 or older have a fasting lipoprotein profile (total cholesterol, LDL cholesterol, HDL cholesterol and triglyceride) done every 5 years. People at higher risk for cardiovascular disease (CVD) or who are on cholesterol-lowering medication will need to have their cholesterol checked more often.

Lipid Testing - A "lipid panel" is taken when cholesterol levels in the blood are tested. Lipids are fats in the blood and include low-density lipoprotein cholesterol (LDL or "bad" cholesterol), high-density lipoprotein cholesterol (HDL or "good" cholesterol) and triglycerides. For the best results, blood should be drawn from a vein in the morning after fasting (nothing to eat or drink) for at least 12 hours. Another blood fat that may be tested is lipoprotein(a), or Lp(a). This is a genetic variation of plasma LDL. Lp(a) may interfere with the body's ability to dissolve blood clots and may play a role in the development of atherosclerosis (fatty buildups in artery walls). High levels of Lp(a) increase the risk for heart disease, heart attack and stroke. Lp(a) is usually checked in those with early-onset heart disease, with family members with early-onset heart disease or in those who have heart disease but don't have the typical risk factors, such as high blood pressure, high cholesterol, etc.

Lipoprotein - The combination of a lipid (fat) surrounded by a protein; the protein allows the fat to travel in the blood. Lipoproteins are characterized by their density: high-density lipoprotein (HDL), low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL). Cholesterol, a building block of the outer layer of cells (cell membranes) is transported through the blood by lipoproteins.

Long QT Syndrome - A condition that affects the heart's electrical system and may cause fast, chaotic heartbeats. It can cause fainting, and in some cases cardiac arrest. The heart's electrical system normally functions by causing the atria (upper chambers) and then the ventricles (lower chambers) to contract. This pattern of normal electrical signals produces a normal ECG (EKG) with Q, R, S, and T waves. In long QT syndrome, the electrical signals are delayed because the electrical system cannot recharge fast enough to carry a signal. This condition increases the risk of a life-threatening arrhythmia known as ventricular tachycardia. People with long QT syndrome may have to limit physical activity, avoid certain medications or have an implantable cardioverter defibrillator (ICD) to prevent sudden death.

Low-Density Lipoprotein (LDL) - A type of protein that transports "bad" cholesterol in the blood. It's the major cholesterol carrier in the blood. (See LDL Cholesterol)

Lp(a) Cholesterol - A genetic variation of LDL cholesterol. Lp(a) is a lipoprotein that resembles LDL in composition with an abnormal protein, termed (a), attached. It can interfere with the body's ability to dissolve blood clots. A high level of Lp(a) is an important risk factor for developing atherosclerosis prematurely. High levels of Lp(a) increase the risk for heart disease, heart attack and stroke. Lp(a) is usually checked in those with early-onset heart disease, with family members with early-onset heart disease or in those who have heart disease but who do not have the typical risk factors, such as high blood pressure, high cholesterol, etc.

Lumen - The open space within a tube, such as a blood vessel.

Magnetic Resonance Imaging (MRI), Nuclear Magnetic Resonance (NMR) Imaging - An imaging procedure that uses powerful magnets to look inside the body. Computer-generated pictures can image the heart muscle and evaluate various heart problems. It can outline the affected part of the brain and help define problems created by stroke. Coronary magnetic resonance angiography (CMRA) combines standard magnetic resonance (MR) imaging with an injection of a chemical dye, called a contrast medium. This allows visualization and precise measurement of blood flow to the heart muscle.

Maze Procedure - A surgical procedure to control atrial fibrillation and/or atrial flutter. A number of incisions are made in the atria to block the path of the arrhythmia.

Minimally Invasive Heart Surgery (MIHS), (Limited Access Coronary Artery Surgery) - An alternative to standard bypass surgery (CABG). Small incisions (ports) are made in the chest. Chest arteries or veins from the leg are attached to the heart to "bypass" the clogged coronary artery or arteries. The instruments are passed through the ports to perform the bypasses. In some cases the surgeon views these operations on video monitors rather than directly.

Mitral Valve - The valve located between the heart's left upper chamber (atrium) and left lower chamber (ventricle). It has two flaps (cusps) that open and close, similar to a double door.

Mitral Valve Prolapse (MVP) - In MVP, one or both valve flaps are enlarged, and some of their supporting "strings" may be too long. When the heart pumps (contracts), the mitral valve flaps don't close smoothly or evenly. Instead, part of one or both flaps collapses backward into the left atrium. This sometimes lets a small amount of blood leak backward through the valve. This may cause a heart murmur. (Also known as Click-Murmur Syndrome, Barlow's Syndrome, Balloon Mitral Valve and Floppy Valve Syndrome.)

Mitral Valve Stenosis - Stenosis literally means narrowing of an opening. Stenosis of the mitral valve limits the forward flow of blood from the heart's left upper chamber (atrium) to the left lower chamber (ventricle). This can cause a backup of blood and fluid in the lungs. Mitral valve stenosis most commonly develops many years after a person has had rheumatic fever, although many people diagnosed with the condition don't recall ever having the illness.

Monounsaturated Fats - A type of fat found in many oils (mostly canola, olive and peanut), nuts and avocados. These fats may help to lower blood cholesterol if used in place of saturated fats. However, mono-unsaturated fats have a lot of calories, so intake should be limited.

Mortality - The total number of deaths from a given disease in a population during an interval of time, usually a year.

Mucocutaneous Lymph Node Syndrome - (See Kawasaki Disease)

Myocardial Biopsy (Endomyocardial Biopsy) - In this test a small amount of tissue is removed from the internal lining of the heart for testing. It is used to help diagnose and treat heart muscle disorders and is also used to detect rejection of the new heart after a heart transplant. A long, flexible tube, called a catheter, is inserted into a vein and threaded up into the heart. The doctor can guide the catheter by watching its movement on a monitor showing an X-ray image of the area. The tip of the catheter is fitted with tiny jaws that the doctor can open and close. Once the catheter is in place, the doctor will take several small snips of muscle for microscopic examination.

Myocardial Infarction - Medical term for heart attack. It is the damaging or death of an area of the heart muscle (myocardium) resulting from a blocked blood supply to that area.

Myocardial Ischemia - A condition in which there is not enough blood flow (and thus oxygen and nutrient supply) to the heart muscle.

Myocardial Perfusion Imaging (MPI) - (See Thallium Stress Test)

Myocarditis - Inflammation of the heart muscle (myocardium).

Myocardium - The muscular center layer of the heart between the outer layer (epicardium) and the inner layer (endocardium). The myocardium is responsible for the heart's pumping action and contracts to pump blood out of the heart and then relaxes as the heart refills with returning blood. The myocardium is the layer that has the largest oxygen needs and is most affected by decreased blood flow (ischemia).

Nitroglycerin - A drug (a vasodilator) that relaxes (dilates) blood vessels and increases the supply of blood and oxygen to the heart while reducing its workload. It's prescribed to patients who can't tolerate ACE inhibitors (another type of medicine that relaxes the blood vessels). "Nitro" is used to treat acute chest pain (angina), in which case it is prescribed as quick-dissolving pills to be placed under the tongue when needed. It can also be prescribed as a routine medication, in which case it is available as slower-release pills, creams or patches. When the blood vessels dilate, blood flow to the tissues increases. This can relieve chest pain.

Norwood Procedure - A complex surgical procedure used for hypoplastic left-heart syndrome (and similar variants) where reconstruction of the absent or small aorta is accomplished by using the patient's own pulmonary artery. This allows unobstructed blood flow to be delivered to the body. As part of the Norwood procedure, the wall between the heart's upper chambers (atria) is removed (atrial septectomy), and a small Gore-tex® tube (shunt) is inserted from the aorta to the pulmonary arteries.

Nurse Practitioner (NP) - An advanced practice nurse with special training and an advanced degree in nursing. Pediatric nurse practitioners (PNPs) may perform examinations, order medications and diagnostic procedures, educate staff and families and provide continuity of care between inpatient and outpatient settings.

Obesity - An excess of body fat. Obesity is defined as a body mass index (BMI) of 30.0 kg/m2 or greater, or about 30 pounds or move over ideal body weight. Extreme obesity is defined as a BMI of 40.0 kg/m2 or more. People who have too much fat, especially in the waist area, are at a higher risk for health problems including high blood pressure, high blood cholesterol, diabetes, heart disease and stroke.

Occluded Artery - An artery in which blood flow has been impaired (occluded) by a blockage.

Occlusion Devices (Atrial and Ventricular Septal Defect Occluders) - A number of investigators are designing devices that can be delivered through a catheter to close holes in the heart's upper chamber (ASDs) and lower chambers (VSDs). A number of these devices have been successfully used in recent clinical trials supervised by the Food and Drug Administration, but the follow-up is quite short at this time.

Open-Heart Surgery - (See Coronary Bypass Surgery)

Overweight - A body mass index (BMI) of 25.0-29.9 kg/m2. A BMI of 25 kg/m2 corresponds to about 10 percent over ideal body weight.