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Why can a ruptured plaque cause a sudden heart attack or stroke?

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The role of coronary artery disease in heart attack — cardiovascular disease This micrograph shows a cross section of a coronary artery narrowed by an atherosclerotic plaque (purplish matter inside the artery). Most heart attacks are caused by the rupture of an atherosclerotic plaque, which triggers the formation of a clot that abruptly blocks blood flow to part of the heart muscle.

A ruptured plaque triggers a sudden heart attack or stroke because it initiates an acute, life-threatening blockage of blood flow.12

When an atherosclerotic plaque ruptures, it exposes the interior of the lesion to the bloodstream, releasing "proclotting" chemicals—most notably tissue factor. This triggers the body's coagulation pathway, causing a blood clot (thrombus) to form rapidly on the surface of the plaque.21

Because this occlusion develops almost instantaneously, the body lacks the time to compensate through mechanisms like collateral circulation. The resulting sudden obstruction prevents oxygenated blood from reaching vital tissues, leading to ischemia and irreversible tissue damage. When this occurs in the coronary circulation, it results in a myocardial infarction (heart attack); when it occurs in the cerebral circulation, it results in a stroke. Notably, these acute events often occur at sites where the plaque had previously narrowed the vessel lumen by only about 50 percent.12