A gradual buildup of fat and cholesterol (plaque) hardens and narrows your arteries (atherosclerosis). Acute coronary syndrome can occur suddenly when this plaque tears or splits open.

A blood clot forms over the opening, narrowing or blocking blood flow to a part of your heart called the myocardium. The heart can’t get enough oxygen. Lack of oxygen (ischemia) damages the heart muscle, leading to unstable angina or heart attack.

Coronary artery spasm and Spontaneous coronary artery dissection (SCAD) can also cause ACS.