Coronary artery disease causes most heart attacks. In coronary artery disease, one or more of the heart (coronary) arteries are blocked. This is usually due to cholesterol-containing deposits called plaques. Plaques can narrow the arteries, reducing blood flow to the heart.

If a plaque breaks open, it can cause a blood clot in the heart.

A heart attack may be caused by a complete or partial blockage of a heart (coronary) artery. One way to classify heart attacks is whether an electrocardiogram (ECG or EKG) shows some specific changes (ST elevation) that require emergency invasive treatment. Your health care provider may use ECG results to describe these types of heart attacks.

• An acute complete blockage of a medium or large heart artery usually means you’ve had an ST elevation myocardial infarction (STEMI).
• A partial blockage often means you’ve had a non-ST elevation myocardial infarction (NSTEMI). However, some people with NSTEMI have a total blockage.

Not all heart attacks are caused by blocked arteries. Other causes include:

• Coronary artery spasm. This is a severe squeezing of a blood vessel that’s not blocked. The artery generally has cholesterol plaques or there is early hardening of the vessel due to smoking or other risk factors. Other names for coronary artery spasms are Prinzmetal’s angina, vasospastic angina or variant angina.
• Certain infections. COVID-19 and other viral infections may cause damage to the heart muscle.
• Spontaneous coronary artery dissection (SCAD). This life-threatening condition is caused by a tear inside a heart artery.

Risk factors

Heart attack risk factors include:

Age. Men age 45 and older and women age 55 and older are more likely to have a heart attack than are younger men and women.

• Tobacco use. This includes smoking and long-term exposure to secondhand smoke. If you smoke, quit.
• High blood pressure. Over time, high blood pressure can damage arteries that lead to the heart. High blood pressure that occurs with other conditions, such as obesity, high cholesterol or diabetes, increases the risk even more.
• High cholesterol or triglycerides. A high level of low-density lipoprotein (LDL) cholesterol (the “bad” cholesterol) is most likely to narrow arteries. A high level of certain blood fats called triglycerides also increases heart attack risk. Your heart attack risk may drop if levels of high-density lipoprotein (HDL) cholesterol — the “good” cholesterol — are in the standard range.
• Obesity. Obesity is linked with high blood pressure, diabetes, high levels of triglycerides and bad cholesterol, and low levels of good cholesterol.
• Diabetes. Blood sugar rises when the body doesn’t make a hormone called insulin or can’t use it correctly. High blood sugar increases the risk of a heart attack.
• Metabolic syndrome. This is a combination of at least three of the following things: enlarged waist (central obesity), high blood pressure, low good cholesterol, high triglycerides and high blood sugar. Having metabolic syndrome makes you twice as likely to develop heart disease than if you don’t have it.
• Family history of heart attacks. If a brother, sister, parent or grandparent had an early heart attack (by age 55 for males and by age 65 for females), you might be at increased risk.
• Not enough exercise. A lack of physical activity (sedentary lifestyle) is linked to a higher risk of heart attacks. Regular exercise improves heart health.
• Unhealthy diet. A diet high in sugars, animal fats, processed foods, trans fats and salt increases the risk of heart attacks. Eat plenty of fruits, vegetables, fiber and healthy oils.
• Stress. Emotional stress, such as extreme anger, may increase the risk of a heart attack.
• Illegal drug use. Cocaine and amphetamines are stimulants. They can trigger a coronary artery spasm that can cause a heart attack.
• A history of preeclampsia. This condition causes high blood pressure during pregnancy. It increases the lifetime risk of heart disease.
• An autoimmune condition. Having a condition such as rheumatoid arthritis or lupus can increase the risk of