A heart attack occurs when one or more of the arteries supplying your heart with oxygen-rich blood (coronary arteries) become blocked. Over time, a coronary artery can become narrowed from the buildup of various substances, including cholesterol and other substances. This buildup — collectively known as plaques — in arteries throughout the body is called atherosclerosis. When your coronary arteries have narrowed due to atherosclerosis, the condition is known as coronary artery disease. Coronary artery disease is the underlying cause of most heart attacks.

During a heart attack, one of these plaques can rupture and spill out cholesterol and other substances into the bloodstream. A blood clot forms at the site of the rupture, partly because the body is confused and is trying to repair the injured blood vessel. If the clot is large enough, it can completely block the flow of blood through the coronary artery.

Another cause of a heart attack is a spasm of a coronary artery that shuts down blood flow to part of the heart muscle. Drugs, such as cocaine, can cause such a life-threatening spasm. A heart attack can also occur due to a tear in the heart artery (spontaneous coronary artery dissection). Other uncommon causes of heart attack include small blood clots or tumors that have traveled from other parts of the body (coronary embolism). Heart attacks can also occur if blood flow to the heart is severely decreased, in situations such as very low blood pressure (shock).

May. 15, 2013