Acute myocardial infarction

Better known as a heart attack, a myocardial infarction is the result of a severe reduction or complete blockage of blood flow to the heart caused by coronary heart disease. Like all muscles in the body, the heart muscle (or myocardium) requires a constant supply of oxygen and nutrients. When a person is healthy, the coronary arteries deliver oxygenated blood to the heart.

But a heart attack can occur when one of the coronary arteries is blocked. These dangerous blockages are usually the result of the buildup of fat-like substances known as plaque due to atherosclerosis. Plaque can eventually tear or rupture, triggering a blood clot to form that blocks the artery and leads to a heart attack. When this happens, it is called a coronary thrombosis or coronary occlusion.

If the blood supply to the heart is cut off severely or for a long time, the cells of the heart muscle suffer irreversible damage and die. Depending on how much heart muscle is damaged or destroyed, a heart attack can result in severe disability or death.

Sometimes, a coronary artery temporarily contracts or goes into spasm. When this happens, the artery narrows and blood flow to part of the heart muscle decreases or stops. What causes a spasm is unclear. But spasms can occur in normal-appearing blood vessels, as well as vessels partly blocked by atherosclerosis. If a spasm is severe enough, a heart attack may result.