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Reviewed by the Faculty of Harvard Medical School

Heart Attack (Myocardial Infarction)

What Is It?

A heart attack occurs when one of the heart's coronary arteries is blocked suddenly, usually by a tiny blood clot (thrombus). The blood clot typically forms inside a coronary artery that already has been narrowed by atherosclerosis, a condition in which fatty deposits (plaques) build up along the inside walls of blood vessels. A heart attack also is called a myocardial infarction or coronary thrombosis.

Each coronary artery supplies blood to a specific part of the heart's muscular wall, so a blocked artery causes pain and malfunction in the area it supplies. Depending on the location and amount of heart muscle involved, this malfunction can seriously interfere with the heart's ability to pump blood. Also, some of the coronary arteries supply areas of the heart that regulate heartbeat, so a blockage sometimes causes potentially fatal abnormal heartbeats, called cardiac arrhythmias. The pattern of symptoms that develops with each heart attack and the chances of survival are linked to the location and extent of the coronary artery blockage.

In 25% of adults, the first sign of heart disease is sudden death from a heart attack. Heart attacks strike approximately 865,000 people in the United States each year, causing more than 179,000 deaths. Because most of these heart attacks result from atherosclerosis, the risk factors for heart attack and atherosclerosis are basically the same:

  • An abnormally high level of blood cholesterol (hypercholesterolemia)
  • An abnormally low level of HDL (high-density lipoprotein), commonly called "good cholesterol"
  • High blood pressure (hypertension)
  • Diabetes
  • Family history of coronary artery disease at an early age
  • Cigarette smoking
  • Obesity
  • Physical inactivity (too little regular exercise)

In early middle age, men have a greater risk of heart attack than women. However, a woman's risk increases once she begins menopause. This could be the result of a menopause-related decrease in levels of estrogen, a female sex hormone that may offer some protection against atherosclerosis.

Although most heart attacks are caused by atherosclerosis, there are rarer cases in which heart attacks result from other medical conditions. These include congenital abnormalities of the coronary arteries, hypercoagulability (an abnormally increased tendency to form blood clots), a collagen vascular disease, such as rheumatoid arthritis or systemic lupus erythematosus (SLE or lupus), cocaine abuse, a spasm of the coronary artery, or an embolus (small traveling blood clot), which floats into a coronary artery and lodges there.


The most common symptom of a heart attack is chest pain, usually described as crushing, squeezing, pressing, heavy, or occasionally, stabbing or burning. Although this pain can occur at any time, a great number of patients experience it in the morning, within a few hours after awakening. Chest pain tends to be focused either in the center of the chest or just below the center of the rib cage, and it can spread to the arms, abdomen, neck, lower jaw or neck. Other symptoms can include sudden weakness, sweating, nausea, vomiting, breathlessness, loss of consciousness, palpitations or confusion. Sometimes, when a heart attack causes burning chest pain, nausea and vomiting, a patient may mistake his or her heart symptoms for indigestion.


Your doctor will ask you to describe your chest pain and any other symptoms. Ideally, a family member or close friend should accompany you when you go for medical treatment. This person can help to provide your doctor with valuable information about your symptoms and medical history if you are unable to do so. It is also important to give your doctor a list of the names and dosages of the prescription and nonprescription medications that you are taking. If you don't have a list already prepared, just scoop the medicines into a nearby bag or purse and bring them with you to the hospital.

Your doctor will suspect that you are having a heart attack based on your symptoms, your medical history and your risk factors for cardiovascular disease. To confirm the diagnosis, he or she will do:

  • An electrocardiogram (EKG)
  • A physical examination, with special attention to your heart and blood pressure
  • Blood tests for serum cardiac markers — chemicals that are released into the blood when the heart muscle is damaged

Additional tests may be needed, including:

  • An echocardiogram — A painless test that uses sound waves to look at the heart muscle and heart valves.
  • Radionuclide imaging — Scans that use special radioactive isotopes to detect areas of poor blood flow in the heart
Expected Duration

How long heart attack symptoms last varies from person to person. In about 15% of cases, the patient never reaches a hospital for treatment and dies quickly after symptoms begin.


You can help to prevent a heart attack by controlling your risk factors for atherosclerosis, especially high blood cholesterol, high blood pressure, smoking and diabetes. If you have high cholesterol, follow your doctor's guidelines for a healthy diet low in fats and cholesterol, and, if necessary, take medication to decrease your blood cholesterol level. If you have high blood pressure, follow your doctor's recommendations for modifying your diet and taking your medication. If you smoke, quit. If you are diabetic, monitor your blood sugar level frequently, follow your diet, and take your insulin or oral medication as your doctor has prescribed. It is also wise to exercise regularly and to maintain an ideal weight.


The treatment of a heart attack depends on how stable the person's condition is and his or her immediate risk of death. Usually, the doctor will give the patient an aspirin to chew in the emergency room, because aspirin helps to prevent blood clotting.

The person also will be given oxygen to breathe, pain medication (usually morphine) for chest pain, beta-blockers to reduce the heart's demand for oxygen, and, if blood pressure is not too low, nitroglycerin to temporarily increase blood flow to the heart. While in the hospital, patients often are given daily beta-blockers, ACE (angiotensin-converting enzyme) inhibitors, which help the heart work more efficiently, primarily by lowering blood pressure, and aspirin. Most heart attack patients also are given a prescription for a cholesterol-lowering medication.

If the diagnosis of heart attack is certain, then the patient will be considered for reperfusion therapy. The goal is to restore blood flow to the injured heart muscle as soon as possible to limit permanent damage. Reperfusion is best done mechanically. The patient is taken to the cardiac catheterization laboratory in the hospital and a catheter is threaded through a large blood vessel toward the heart. Dye is injected to locate the blockage in the coronary artery.

The next step is percutaneous transluminal coronary angioplasty (PTCA). In PTCA, a different catheter that has a small deflated balloon is threaded past the blockage, and the balloon is inflated to crush the clot and plaque. Most balloon catheters also have a wire mesh, called a stent, over the balloon. After the balloon is inflated to unclog the blocked artery, the stent remains in place to keep the artery open. Newer drugs called IIb/IIIa receptor inhibitors reduce clotting even more powerfully than aspirin. These drugs have been shown to be beneficial in patients who are about to undergo PTCA or stent placement. They include abciximab (ReoPro) and tirofiban (Aggrastat).

Reperfusion therapy can also be done with clot-dissolving drugs called thrombolytic agents. These include tissue plasminogen activator (tPA), streptokinase (Streptase), and anisoylated plasminogen streptokinase activator complex (APSAC). These drugs are often used if it would take too long to transfer a patient to a hospital where an angioplasty could be performed.

Much of the additional treatment for heart attack depends on whether the patient developed any complications. For example, additional drugs may be needed to treat dangerous cardiac arrhythmias (abnormal heartbeats), low blood pressure, and congestive heart failure.

When To Call A Professional

Seek emergency help immediately if you have chest pain, even if you think it is just indigestion or that you are too young to be having a heart attack. Prompt treatment increases your chance of limiting heart muscle damage, because reperfusion measures work best if they are started within 30 minutes after symptoms start.


About 15% of patients who suffer a heart attack die before they reach a hospital, and another 15% die after they arrive. Among the remaining 70% who survive hospitalization, about 4% (1 in 25) will die within the first year after discharge. However, this risk is not the same for all age groups. For example, for patients older than 65, the death rate is 20% within the first month after a heart attack, and 35% within the first year.

Additional Info

National Heart, Lung and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD 20824-0105
Phone: 301-592-8573
TTY: 240-629-3255
Fax: 240-629-3246

American Heart Association (AHA)
7272 Greenville Ave.
Dallas, TX 75231
Toll-Free: 1-800-242-8721

Last updated March 30, 2009