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.