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Myocardial Infarction


Figure A shows damage (dead heart muscle) caused by a heart attack. (

A heart attack is a life-threatening medical emergency that requires immediate treatment. A heart attack, also known as a myocardial infarction (MI), happens when arterial flow of blood that brings oxygen to a region of heart muscle suddenly becomes blocked. Heart muscle cells will die if blood flow is not restored. The longer the heart goes without enough oxygen, the more damage is done to the heart muscle. According to the CDC, more than 800,000 people in the United States have a heart attack each year.


Most heart attacks are caused by coronary artery disease (atherosclerosis).  Age, lifestyle habits, and other medical conditions raise the risk of a heart attack. Symptoms of a heart attack include chest and upper body pain, shortness of breath, dizziness, sweatiness, and nausea. Women often experience different symptoms of a heart attack.


The most common cause of a heart attack is arterial thrombosis resulting from coronary artery disease (CAD). Most of the time, CAD happens when a substance called plaque builds up inside coronary arteries, causing the arteries to narrow. The buildup of this plaque is called atherosclerosis. This can happen over many years, and it can block blood flow to parts of your heart muscle. Plaque that narrow arteries slowly over time causes angina. An area of plaque can rupture inside a coronary artery. This causes a blood clots to form on the plaque’s surface. If the clot becomes large enough, it can block arteries providing blood flow to the heart. If the blockage isn’t treated quickly, a part of the heart muscle begins to die.​

Not all heart attacks are caused by blockages from atherosclerosis. When other heart and blood vessel conditions cause a heart attack, it is called myocardial infarction in the absence of obstructive coronary artery disease (MINOCA). A sudden and serious spasm (tightening) of your coronary artery can block blood flow through coronary arteries, even if there isn’t a buildup of plaque. Smoking is a risk factor for a coronary spasm. Smokers may be more likely to have a spasm triggered by extreme cold or very stressful situations. Drugs like cocaine may also cause coronary spasm. A coronary artery embolism occurs when a blood clot travels through the bloodstream and gets stuck in a coronary artery. blocking blood flow. This is more common in people who have atrial fibrillation or conditions that raise the risk of blood clots, such as thrombocytopenia or pregnancy. Spontaneous coronary artery dissection (SCAD) occurs when a tear forms inside your coronary artery. A blood clot can then form at the tear, or the torn tissue itself can block the artery. SCAD can be caused by stress, extreme physical activity, and pregnancy. This condition is more common in women who are under 50 years old or pregnant and in people who have Marfan syndromeAdditional information on myocardial infarction can be found from the NHLBI (

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