A heart attack occurs when blood flow to a section of heart muscle becomes blocked. If the flow of blood isn’t restored quickly, the healthy tissue of the heart muscle becomes damaged from lack of oxygen and begins to die. This is also called a myocardial infarction, MI.

Heart attacks occur most often as a result of a condition called coronary artery disease (CAD). In coronary artery disease, a fatty material called plaque builds up over many years on the inside walls of the coronary arteries (the arteries that supply blood and oxygen to your heart). Eventually, an area of plaque can rupture, causing a blood clot to form on the surface of the plaque. If the clot becomes large enough, it can mostly or completely block the flow of oxygen-rich blood to the part of the heart muscle fed by the artery, myocardial infarction.

Heart With Muscle Damage and a Blocked Artery

Figure A is an overview of a heart and coronary artery showing damage (dead heart muscle) caused by a heart attack. Figure B is a cross-section of the coronary artery with plaque buildup and a blood clot.

During a heart attack or MI, if the blockage in the coronary artery isn’t treated quickly, the heart muscle will begin to die and be replaced by scar tissue. This heart damage may not be obvious, or it may cause severe or long-lasting problems.

Severe problems linked to heart attack can include heart failure and life-threatening arrhythmias. Heart failure is a condition in which the heart can’t pump enough blood throughout the body. Ventricular fibrillation is a serious arrhythmia that can cause death if not treated quickly.