What Causes a Heart Attack?

Most heart attacks occur as a result of coronary artery disease (CAD). CAD is the buildup over time of a material called plaque on the inner walls of the coronary arteries. Eventually, a section of plaque can break open, causing a blood clot to form at the site. A heart attack occurs if the clot becomes large enough to cut off most or all of the blood flow through the artery.

Coronary Artery With Plaque Buildup

The illustration shows a normal artery with normal blood flow (figure A) and an artery containing plaque buildup (figure B).

The blocked blood flow prevents oxygen-rich blood from reaching the part of the heart muscle fed by the artery. The lack of oxygen damages the heart muscle. If the blockage isn’t treated quickly, the damaged heart muscle begins to die.

Heart attack also can occur due to problems with the very small, microscopic blood vessels of the heart. This condition is called microvascular disease. It’s believed to be more common in women than in men.

Another less common cause of heart attack is a severe spasm (tightening) of a coronary artery that cuts off blood flow through the artery. These spasms can occur in coronary arteries that don’t have CAD. It’s not always clear what causes a coronary artery spasm, but sometimes it can be related to:

• Taking certain drugs, such as cocaine
• Emotional stress or pain
• Exposure to extreme cold
• Cigarette smoking

The animation below shows how a heart attack occurs. Click the “start” button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.

The animation shows how blood flow is blocked in the heart, leading to a heart attack.