A heart attack is generally brought on after the blood supply to part of the myocardium, or the heart muscle, is severely reduced or stopped. This usually means that either one or more of the coronary arteries which supply blood to the heart muscle, are blocked.

The cause of a blockage is usually plaque, which is deposits of fat-like substances, and the name of this process is called atherosclerosis. The plaque usually eventually bursts or ruptures and this can cause a 'snag' where blood clots can form and they block the arteries. This then leads to a heart attack.

If a heart attack lasts for longer than a few minutes, it is possible for the person to become disabled or they could even die. This is because the body cannot survive for very long without the heart and the heart relies upon the blood to keep it pumping. So depending upon how long the blood supply is stopped for, determines just how badly affected the person will be after the attack.