The heart muscle works non-stop and needs a steady supply of oxygen-rich blood. Three major coronary vessels on the heart's surface supply this blood. A heart attack happens when blood flow through a coronary artery is suddenly blocked.
Heart attacks are also called myocardial infarction (or MI). ("Myo" means muscle; "cardio" means heart; and "infarction" means tissue death due to lack of oxygen, or ischemia.) Most often, a heart attack is caused by a blood clot in a coronary artery that is narrowed by plaque (atherosclerosis). This plaque builds up gradually over the years but it can break open suddenly, like a torn scab, exposing a rough surface that attracts blood platelets and clots. Less commonly, a heart attack can also happen when a coronary artery goes into spasms, pinches the vessel shut, and cuts off blood flow. If blood flow is not restored quickly after a clot or spasm, part of the heart muscle may starve and die. This can lead to cardiogenic shock, heart failure, arrhythmias, valve dysfunction, an embolism (clot that travels to the brain or lung) or death. The extent of the heart damage and health consequences depend on which vessel is blocked and how long it remains blocked.