What causes a heart attack?

By: Elizabeth Scherer

The most common cause of heart attack is the sudden blockage of one of the heart's arteries by a blood clot. These clots typically form in arteries that are already affected by atherosclerosis - that is, the arteries are narrowed by fatty deposits of plaque and other materials.

How Does Atherosclerosis Cause a Heart Attack?

Atherosclerosis can cause a heart attack in one of three ways.


  • The fatty plaque can cut off blood supply by completely blocking a coronary artery.
  • The plaque can tear or rupture, causing a blood clot to form. The blood clot may become large enough to close off the artery. This type of heart attack is called a coronary thrombosis or coronary occlusion.
  • Narrowed arteries may not be able to supply enough oxygen-rich blood. This could cause the heart to beat with an abnormal rhythm called an arrhythmia.

What else might cause a heart attack?

Sometimes heart attacks occur when an artery goes into a temporary spasm, cutting off blood supply to the heart. If the spasm is severe enough, it can cause a heart attack. The cause of these spasms isn't understood. They can occur both in blood vessels that appear normal and in vessels that are partially blocked by plaque.

In rare cases, heart attacks may be the result of other conditions. These could include the following:

  • an abnormal tendency of the blood to clot called hypercoagulability
  • collagen vascular disease such as rheumatoid arthritis or systemic lupus erythematosus
  • cocaine use
  • a small traveling blood clot called an embolus that gets stuck in a coronary artery

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