Ablation: Procedure that eliminates extra electrical pathways within the heart that cause fast or irregular heart rhythms.

AED: Automated External Defibrillator. A portable, user-friendly electronic device that automatically diagnoses potentially life-threatening heart rhythms and, if necessary, permits a shock to be delivered to restore a normal heart rhythm. Also known as simply a defibrillator.

Aneurysm: Small pouches on blood vessel walls. The blood vessel or area of the heart is thin or weakened in this area. They can rupture (break), causing bleeding.

Angina: A recurring pain or discomfort in the chest area. This discomfort is caused by some part of the heart not receiving enough blood. The pain can feel like heaviness, a burning sensation or a discomfort in the left arm or jaw.

Aorta: The largest artery in the body, and the primary blood vessel that carries oxygenated blood out of the heart to the rest of the body.

Aortic Regurgitation: A backwards leakage of blood from the aorta, through a weakened aortic valve, into the left ventricle. This results in stress in the left side of the heart and an inadequate blood flow to the body.

Aortic Stenosis: A narrowing of the opening of the aortic valve, the valve that regulates blood flow from the left ventricle of the heart into the aorta.

Arrhythmia: An abnormal heart rhythm. Also known as dysrhythmia.

Arrhythmogenic Right Ventricular Dysplasia (ARVD): A rare condition that produces ventricular tachycardia. In this disease ventricular muscle is replaced by fatty and fibrous tissue for unknown reasons. It is emerging as a cause of sudden cardiac death (SCD) in young otherwise healthy adults.

Artery: A blood vessel which carries oxygen rich blood away from the heart to the body. The major arteries of the heart are called the coronary arteries.

Atherosclerosis: A buildup of cholesterol or other fatty deposits called plaque that can occur on the inner walls of blood vessels and arteries, which in advanced stages causes restriction or blockage of blood flow to the heart or brain.

Atrial Fibrillation: A very fast and irregular beating or quivering of the upper two chambers of the heart. This condition happens just before a cardiac arrest or just as the heart stops all together.

Atrial Flutter: A rapid rhythm driven by pacemaker activity in atrial sites other than the SA node (the natural pacemaker).

Atrial Septal Defect: A small hole in the septum or top part of the heart. Also known as ASD.

Atrioventricular Block: An interruption of the electrical signal between the atria and the ventricles.

Atrioventricular Nodal Reentrant Tachycardia (AVRT): A supraventricular tachycardia caused by dual conduction pathways within the AV node which have different speeds of transmission.

Automated External Defibrillator: see AED