Blood cells: The solid elements of the blood. Red blood cells carry oxygen to the tissues; white blood cells combat disease-causing agents by destroying them, or by stimulating the body's natural defense systems; platelets contribute to clotting.

Blood clot: A firm mass composed of blood cells, fibrin, and platelets.

Blood pressure: Force or pressure that circulating blood exerts on the walls of the arteries; divided into systolic (during heart contraction) and diastolic (during heart relaxation) pressures.

Blood vessels: The hollow tubes that carry blood throughout the body. The blood vessels include arteries, veins, arterioles, venules, and capillaries.

Bradycardia: Slow heart beat, usually below 60 beats per minute.

CAD: See Coronary artery disease.

Calcification: Depositing of calcium; in atherosclerosis, calcification of plaques results in hard, brittle arterial walls.

Capillaries: Tiny vessels that connect arterioles and venules; the exchange of nutrients and fluids between the tissues and blood occurs through the walls of these vessels.

Cardiac catheterization: Passage of a small tube (catheter) through a vein in the arm, leg, or neck into the heart.

Cardiac imaging study: Diagnostic technique that provides images of heart structure and function; includes chest x-ray films, coronary angiography, thallium 201 imaging, acute infarct scintigraphy, radionuclide ventriculography, and echocardiography.

Cardiomyopathy: A type of heart disease that affects the heart muscle (myocardium). This type of disorder may result in problems with how the heart pumps blood.

Cardiovascular: Pertaining to the heart and blood vessels.

Cardiovascular Disease: Any disorder that affects the heart muscle or the blood vessels of the heart. It includes any condition that impacts the blood vessels, such as poor circulation due to blockage.

Cholesterol: A fatty substance found in cell membranes; plays an important role in essential body functions.

Chronic stable angina: Recurrent episodes of angina (chest pain) that are related to exertion and do not change in frequency, severity, or duration.

Chronic venous insufficiency: Condition in which veins do not channel the flow of blood adequately. Most often seen in the lower extremities.

Clotting: The process by which fluid blood changes to a solid.

Clotting cascade: The series of cellular and molecular reactions among blood clotting factors that cause clotting; also called coagulation cascade.

Clotting factors: A group of chemicals in the blood (factors I to XIII) that interact to make blood clot.

Coagulation: Blood clotting; formation of a blood clot.

Coarctation: Narrowing of a blood vessel, such as the congenital condition coarctation of the aorta.

Congenital heart disease: Disorders resulting from incomplete development of the heart in the womb; birth defects of the heart.

Congestive heart failure: Heart failure resulting from impaired pumping, causing blood to back up and accumulate in the blood vessels or lungs; also called CHF.

Coronary angiography: Heart imaging study that shows the shape of the coronary arteries and areas that are narrowed or blocked.

Coronary arteries: Arteries that supply oxygen and nutrient-rich blood to the tissues of the heart itself.

Coronary artery bypass grafting: Surgical procedure used to restore blood flow to a part of the heart; a blood vessel from the patient's leg or chest is grafted to a coronary artery to bypass an obstructed area of the artery; also called CABG.

Coronary artery disease (CAD): Disease characterized by atherosclerosis of the coronary arteries; may cause angina pectoris and myocardial infarction; also called CAD.

Deep vein thrombosis: Formation of blood clots in the deep veins of the extremities; also called DVT.

Deep veins: Veins located deep within the muscles.

Defibrillation: Use of drugs or an electric shock to stop the fibrillation (rapid uncoordinated twitching movements) of the heart and restore normal rhythm.

Diastole: Period in the cardiac cycle during which the heart muscle relaxes and fills with blood.

Dilated cardiomyopathy: Group of disorders in which the heart muscle is weakened and cannot pump effectively. The result is dilation of the heart chambers or enlargement of the heart. Poor cardiac function results in congestive heart failure.

DVT: See Deep Vein Thrombosis.

Dyspnea: Difficulty breathing; often results in shortness of breath.

Echocardiography: Cardiac imaging study that uses sound waves to create images of the heart; shows heart's motion and size of its chambers.

Edema: Swelling caused by an excess of fluid accumulation.

Electrocardiogram: Graphic recording of the electrical activity of the heart; detects and records the electrical potential of the heart during contraction; also called ECG or EKG.

Embolism: Sudden blockage of an artery by a clot or foreign material carried and deposited by the blood current.

Embolus: Blood clot that causes embolism.

Exercise stress test: Noninvasive diagnostic procedure in which a patient exercises while undergoing ECG monitoring; can detect exercise-induced ischemia (lack of blood supply).

Fibrin: A protein necessary for blood clotting; fibrin forms a web-like mesh that traps platelets and red blood cells and holds a clot together.

Heart: The hollow muscular organ that pumps blood throughout the body.

Heart attack: Heart cell death due to prolonged lack of oxygen; also called myocardial infarction or MI.

Heart failure: Disease state caused by impaired pumping of the heart.

Hematocrit: The relative volume of red blood cells to the volume of whole blood; also, the instrument for measuring this ratio .

Hemoglobin: Oxygen-transporting component of red blood cells.

Hemostasis: Stopping of bleeding through natural (clot formation, constriction of blood vessels), artificial (compression, ligation), or surgical means.

Heparin: An anticoagulant commonly used to prevent the formation of new blood clots (rethrombosis) in the acute myocardial infarction (MI) patient; also used to prevent blood clotting during open-heart surgery.

Heparinoids: Agents having anti-clotting activity resembling that of a heparin.

Hyperglycemia: Abnormally high levels of glucose (sugar) in the blood.

Hypertension: Persistently high blood pressure; may have no known cause (essential or idiopathic) or result from other primary diseases (secondary). It is a risk factor for heart disease, peripheral vascular disease, stroke, and kidney disease.

Hypoplastic heart: Form of congenital heart disease in which one side of the heart is incompletely formed.

Hypotension: Abnormally low blood pressure.

Infarction: Cell death due to insufficient supply of oxygen.

Ischemia: Insufficient supply of blood and oxygen to a part of the body; often results from constriction or obstruction of a blood vessel.

Ischemic heart disease: Disturbance of heart function resulting from inadequate supply of oxygen to the heart muscle; also called coronary artery disease (CAD) and IHD.

Low-molecular-weight heparins: An anticoagulant medication used to prevent the formation of new blood clots; it is one-third the size of heparin; potential advantages include once-a-day dosing and no need for laboratory monitoring.

Mitral stenosis: Congenital (present at birth) or acquired abnormality of the mitral valve in the heart; narrowing and ineffective opening of the mitral valve.

Mitral valve: Heart valve that separates the left atrium from the left ventricle. When the atrium contracts, the valve opens to allow blood into the ventricle. On closure, the mitral valve prohibits the flow of blood back into the atrium.

Mitral valve prolapse: Abnormality affecting the mitral valve, often with flow of blood back into the atrium; characterized by systolic clicks and murmurs.

Myocardial cells: Heart muscle cells; cells found in the myocardium.

Myocardial infarction: Heart cell death due to prolonged lack of oxygen; also called MI or heart attack.

Myocardium: Middle and thickest layer of the heart wall.

Orthostatic hypotension: Drop in blood pressure brought on by changes in body position, such as rising from a chair or bed.

Patent ductus arteriosus: Condition in which ductus arteriosus (hole between aorta and pulmonary artery) remains open (patent); usually closes within hours after birth; prevents transport of blood and nutrients to the body.

Pericardial effusion: Collection of fluid or blood in the sack (pericardium) that surrounds the heart. Causes include congestive heart failure, cancer, and autoimmune disease.

Pericardial tamponade: A life-threatening syndrome in which fluid (usually blood) collects in the sack (pericardium) that surrounds the heart and interferes with its performance. Untreated, condition can result in low blood pressure, shock, and death.

Plaque: Buildup of cholesterol and fatty material within an artery wall occurring in atherosclerotic disease. Also called atherosclerotic plaque.

Plasma: Liquid portion of the blood; remains after cells have been removed.

Platelets: Oval cells found in the blood and involved in clotting; also called thrombocytes.

Precordial: Pertaining to the precordium, which is the region over the heart and stomach.

Preload: The pressure inside the left ventricle at the end of diastole; determined by venous return and myocardial contractility and relaxation.

Pulmonary artery: Artery that carries deoxygenated blood from the right ventricle of the heart to the lungs.

Pulmonary edema: Severe state of increased fluid within the lung, leading to flooding of the alveoli; often result of ineffective pump function of the heart, but noncardiac causes also exist.

Pulmonary embolism: Lodging of a blood clot in the lumen (open cavity) of a pulmonary artery, causing a severe dysfunction in respiratory function. Pulmonary emboli often originate in the deep leg veins and travel to the lungs through blood circulation. Symptoms include sudden shortness of breath, chest pain (worse with breathing), and rapid heart and respiratory rates.

Pulmonary stenosis: A congenital (present at birth) or acquired heart valve defect, characterized by abnormal narrowing and ineffective opening of the pulmonary valve. Symptoms include cyanosis (bluish discoloration of the skin) and difficulty breathing.

Refractory angina: Chest pain that does not respond to pharmacologic therapy.

Renal artery stenosis: Narrowing of the renal artery or one of its main branches.

Spasm: Abnormal contraction of vascular smooth muscle that causes narrowing of blood vessels.

Stasis: The slowing of blood flow.

Stenosis: Narrowing of the inside of a blood vessel.

Sternum: The breastbone.

Stress tests: Noninvasive procedure used to provoke and detect myocardial ischemia, either through the use of exercise or pharmacologic agents.

Stroke: Death of tissue within the central nervous system resulting from a clot blocking a blood vessel in the brain or from hemorrhaging caused by a ruptured blood vessel on the surface or within the brain.

Subcutaneous: Given or occuring under the skin.

Superficial veins: Veins lying close to the surface of the skin.

Systole: Period of the cardiac cycle during which the heart muscle contracts and pumps blood out and into the arteries.

Systolic blood pressure: Pressure exerted on the walls of the arteries during the contraction phase of the heartbeat; varies with age, gender, size, and physical condition.

Tachycardia: Excessively rapid heat rate, usually above 100 beats per minute.

Thallium heart scan: Diagnostic test that involves the introduction of a radioactive tracer into the bloodstream to determine blood flow.

Thallium stress test: Diagnostic test used to assess coronary blood flow before and after strenuous exercise. A radioactive tracer is introduced into the bloodstream and measured with a special camera.

Thrombocytopenia: A condition in which there is an abnormally small number of platelets in the circulating blood; usually associated with bleeding conditions.

Thromboembolism: Obstruction of a blood vessel with material deposited by the bloodstream.

Thrombolytic agents: Medicines used to dissolve blood clots formed in certain blood vessels.

Thromboprophylaxis: The use of drugs or other protective therapies to reduce thrombosis.

Thrombosis: Formation of thrombosis (blood clot) within the lumen (open cavity) of the blood vessels or heart.

Thrombus: Blood clot formed from platelets and other elements; may obstruct a blood vessel at its point of formation or travel to other areas of the body.

Tissue factor: A protein released from damaged tissue that triggers the clotting cascade.

Unstable angina: Form of angina pectoris (chest pain) characterized by sudden changes in the severity or length of attacks.

Unstable plaque: Plaque that is prone to rupture, causing release of fat from within the plaque into the inside of the artery.

Valves: Cup-like folds inside a vein that prevent backward flow of blood. Valves open as blood moves through them and close under the weight of blood collecting in the vein due to low pressure and gravity.

Varicose: Unnaturally and permanently distended; usually refers to veins.

Vascular endothelium: Layer of cells that lines the blood vessels and is in direct contact with blood.

Veins: Thin-walled vessels that carry deoxygenated blood to the heart (the pulmonary vein is the only exception).

Venous insufficiency: A condition in which the veins do not channel the flow of blood adequately; most often seen in the lower extremities.

Ventricles: Two lower chambers of the heart.

Ventricular arrhythmia: Cardiac arrhythmia originating within the ventricles; isolated ventricular contractions are referred to as premature ventricular contractions. Frequent premature ventricular contractions can be potentially unstable and can degrade to a more serious rhythm or cardiac arrest.

Ventricular tachycardia: Abnormal heart beat in the lower chambers of the heart, usually to a rate of 150-200 beats per minute; may result in fainting, low blood pressure, shock, or even sudden death; common and often lethal complication of heart attack.

Venules: Small veins.

Vital signs: Pulse, blood pressure, and respiration.