Advance Directive (living will): A document written in "good" health which informs your family and health care providers of your wishes for extended medical treatment in times of emergency.

Aerobic Exercise: Exercise which can improve your functional ability and, in some cases, reduce symptoms of heart disease. It is repetitive in nature and involves the large muscle groups. Examples are walking, swimming, and cycling.

Ambulatory Monitors: Small portable electrocardiograph machines that are able to record the heart's rhythm. Each type of monitor has unique features related to length of recording time and ability to send the recordings over the phone. Types of ambulatory monitors include: Holter Monitor, Loop Recorder, and Transtelephonic transmitter.

Anemia: A condition characterized by a deficiency of red blood cells. Anemia reduces the amount of oxygen available to the body.

Aneurysm: A sac formed by the bulging of a blood vessel wall or heart tissue. When aneurysms grow too large, they can rupture and the bleeding can be life threatening. Aneurysms that have grown too large should be removed.

Angina (also called angina pectoris): Discomfort or pressure, usually in the chest, caused by a temporarily inadequate blood supply to the heart muscle. Discomfort may also be felt in the neck, jaw, or arms.

Angiogenesis: The spontaneous or drug-induced growth of new blood vessels. The growth of these vessels may help to alleviate coronary artery disease by rerouting blood flow around clogged arteries.

Angioplasty: An invasive procedure, during which a specially designed balloon catheter with a small balloon tip is guided to the point of narrowing in the artery. Once in place, the balloon is inflated to compress the fatty matter into the artery wall and stretch the artery open to increase blood flow to the heart.

Angiotensin-Converting Enzyme Inhibitors (ACE inhibitors): A group of drugs used to treat high blood pressure and heart failure. ACE inhibitors block a specific enzyme (ACE or angiotensin-converting enzyme) that retains salt in the kidney and can cause heart and blood pressure problems. ACE inhibitors have been shown to decrease the risk of dying from a heart attack.

Angiotensin II Receptor Blockers (ARBs): A group of drugs used to treat high blood pressure.

Annulus: A ring of tough fibrous tissue that is attached to and supports the leaflets of the heart valve.

Anomalous Coronary Artery: The normal anatomy for the coronary arteries involves their origin from the aorta at each of two separate sites. Sometimes people can be born with the origin of a coronary artery that comes from an abnormal site and this can lead to problems of coronary ischemia which can subsequently lead to a heart attack. Not all coronary anomalies need surgery, but some do and the specific operation depends on which of the many varieties of coronary anomalies is present.