Coronary Artery Disease (CAD) is the most common type of heart disease and occurs when the arteries that supply blood to the heart muscle (coronary arteries) become hardened and narrowed.

When blood flow and oxygen supply to the heart are reduced or cut off, you can develop either angina or heart attack. Angina is chest pain or discomfort that occurs when your heart is not getting enough blood. For more information on Angina see National Heart, Lung and Blood Institute (NHLBI) website. A heart attack happens when a blood clot suddenly cuts off most or all blood supply to part of the heart. Cells in the heart muscle that do not receive enough oxygen-carrying blood begin to die. This can cause permanent damage to the heart muscle. It is also known as Myocardial infarction or MI, Acute myocardial infarction or AMI, Acute coronary syndrome, Coronary thrombosis or Coronary occlusion. Myocardium is a part of the heart muscle and as it may die (infarct) it is called myocardial infarction (MI).

As per the NHLBI website (Aug 2003), each year, more than a million persons in the U.S. have a heart attack and about half (515,000) of them die. About one-half of those who die do so within 1 hour of the start of symptoms and before reaching the hospital. When a heart attack is suspected it is better to obtain emergency help than to wait.