The heart is one of the largest muscles in the body. The wall of the heart is the muscle that does the pumping, and it is called the myocardium. In a heart attack, this muscle tissue is denied oxygen-carrying blood due to a blocked artery. When the shortage of oxygen gets so bad that many cells die, it's called infarction. The medical name for a heart attack is an acute myocardial infarction (MI).
1.25 million Americans experience one or more heart attacks every year, and about a third of these people die. Although having a heart attack is very serious, the chances of survival are greatly increased if you are able to get to a hospital right away.
Every organ needs oxygen-carrying blood to stay alive, and the myocardium (the muscle that forms the wall of the heart) is no exception. It has its own oxygen supply, via the coronary arteries. In coronary artery disease, fatty deposits (plaques) form in the inner walls of the coronary arteries, narrowing them and reducing blood flow to the heart. This process is called atherosclerosis.
Most heart attacks occur when the atherosclerotic plaque lining an artery ruptures. Blood then forms a clot on the damaged artery, which may partially or completely obstruct blood flow. If the blockage gets severe enough, heart attack symptoms appear, and heart muscle cells may start to die. This is now considered a heart attack.
Rarely, a coronary artery spasm stops blood flow through an apparently healthy coronary artery, causing a heart attack. In most of these cases there's no identifiable cause.