Plaque is a buildup of cholesterol, white blood cells, calcium, and other substances in the walls of arteries. Over time, plaque narrows the artery, and the artery hardens (atherosclerosis).

Plaque sometimes reduces blood flow to the heart muscle, which can cause angina symptoms, such as chest pain or pressure. Plaque in the large artery in the neck (carotid artery stenosis) may reduce blood flow to the brain.

Plaques are covered with a fibrous cap, which may rupture if some trigger causes a surge in blood pressure or causes the artery to constrict. A person may have a heart attack or stroke if a plaque breaks open, creating a blood clot that completely blocks blood flow through the artery.