A heart attack is the death of, or damage to, part of the heart muscle because the supply of blood to the heart muscle is severely reduced or stopped.

Also called myocardial infarctions, heart attacks are the leading cause of death in the United States. Each year, more than 1.5 million Americans suffer an attack, and almost half a million die. Most heart attacks follow years of silent but progressive coronary artery disease, which can be prevented in many people. A heart attack is often the first symptom of coronary artery disease. According to the American Heart Association, 63% of women and 48% of men who die suddenly of coronary artery disease had no previous symptoms.

A heart attack occurs when one or more of the coronary arteries that supply blood to the heart is completely blocked, cutting off blood to the heart muscle. The blockage is usually caused...