A heart attack is when blood vessels that supply blood to the heart are blocked, preventing enough oxygen from getting to the heart. The heart muscle dies or becomes permanently damaged. Your doctor calls this a myocardial infarction.

Myocardial infarction; MI; Acute MI; ST-elevation myocardial infarction; non-ST-elevation myocardial infarction

Most heart attacks are caused by a blood clot that blocks one of the coronary arteries. The coronary arteries bring blood and oxygen to the heart. If the blood flow is blocked, the heart starves for oxygen and heart cells die.

In atherosclerosis, plaque builds up in the walls of your coronary arteries. This plaque is made up of cholesterol and other cells. A heart attack can occur as a result of the following:

• The slow buildup of plaque may almost block one of your coronary arteries. A heart attack may occur if not enough oxygen-containing blood can flow through this blockage. This is more likely to happen when you are exercising.
• The plaque itself develops cracks (fissures) or tears. Blood platelets stick to these tears and form a blood clot (thrombus). A heart attack can occur if this blood clot completely blocks the passage of oxygen-rich blood to the heart.

Occasionally, sudden overwhelming stress can trigger a heart attack.

Risk factors for heart attack and coronary artery disease include:

• Increasing age (over age 65)
• Male gender
• Diabetes
• Family history of coronary artery disease (genetic or hereditary factors)
• High blood pressure
• Smoking
• Too much fat in your diet
• Unhealthy cholesterol levels, especially high LDL ("bad") cholesterol and low HDL ("good") cholesterol
• Chronic kidney disease

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Goodman SG, Menon V, Cannon CP, Steg G, Ohman EM, Harrington RA, et al. Acute ST-segment elevation myocardial infarction: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th edition). Chest. 2008;133:708S-775S.