Drug Information

Aspirin for Heart Attack and Unstable Angina

Aspirin for Heart Attack and Unstable Angina


Generic Name Brand Name
acetylsalicylic acid (aspirin) Asaphen, Aspirin, Entrophen, Novasen

How It Works

Aspirin slows the blood’s clotting action by reducing the clumping of platelets. Platelets are cells that clump together and help to form blood clots. Aspirin keeps platelets from clumping together, thus helping to prevent or reduce blood clots.

During a heart attack. Blood clots form in an already-narrowed artery and block the flow of oxygen-rich blood to the heart muscle. When taken during a heart attack, aspirin slows clotting and decreases the size of the blood clot that is forming.

After a heart attack. Aspirin can help prevent a second heart attack. Taken daily, aspirin’s anti-clotting action helps prevent a first or second heart attack.

Why It Is Used

For people who are having a heart attack. You can take aspirin to help you during a heart attack. After you call 911 or other emergency services, the operator may tell you to chew 1 adult-strength or 2 to 4 low-dose aspirin. Or you might be given aspirin in the ambulance or emergency room. Aspirin slows blood clotting. So a blood clot that is causing the heart attack stays smaller.

For people who have had a heart attack. Aspirin can help prevent a second heart attack.

For people who have never had a heart attack. Aspirin may reduce your chance of having a heart attack or a stroke if you have certain risk factors, such as diabetes, high blood pressure, high cholesterol, or smoking. If you have a higher risk for a heart attack or stroke, aspirin will have even more benefit for you.

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Low-dose aspirin may also be used by people who have:

  • Coronary artery disease .
  • Stable angina .
  • Unstable angina
  • Had bypass surgery  or angioplasty .
  • Had a stroke  or transient ischemic attack  (TIA).

But in people with a relatively low risk for cardiovascular disease, the benefits of preventive aspirin therapy may be outweighed by the increased risk of bleeding problems.

How Well It Works

  • Aspirin can lower the risk of a first heart attack and recurrent heart attacks.
  • Aspirin may reduce the severity of a heart attack when taken immediately after symptoms begin.
  • Aspirin may help improve the symptoms of unstable angina.
  • Aspirin may lower the risk of death caused by heart disease.

Generic or store brands are as effective as brand-name aspirin.

Side Effects

All medicines have side effects. But many people don’t feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.

Here are some important things to think about:

  • Usually the benefits of the medicine are more important than any minor side effects.
  • Side effects may go away after you take the medicine for a while.
  • If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.
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Allergic reaction

Call 911 or other emergency services right away if you have:

  • Trouble breathing.
  • Swelling of your face, lips, tongue, or throat.

Call your doctor if you have:

  • Hives.


Call 911 or other emergency services right away if you have:

  • A sudden, severe headache that is different from past headaches. (It may be a sign of bleeding in the brain.)

Call your doctor now or seek medical care if:

  • You have any abnormal bleeding, such as:
    • Nosebleeds.
    • Vaginal bleeding that is different (heavier, more frequent, at a different time of the month) than what you are used to.
    • Bloody or black stools, or rectal bleeding.
    • Bloody or pink urine.

Common side effects of this medicine include:

  • Stomach pain or discomfort.
  • Nausea.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

For more information about taking daily aspirin, see the topic Low-Dose Aspirin Therapy.

If you have had a heart attack or stroke, your doctor has probably already prescribed aspirin for you.

If you do not take aspirin, talk to your doctor before you start taking aspirin every day.

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Taking medicine

Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don’t take your medicines properly, you may be putting your health (and perhaps your life) at risk.

There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.

Advice for women

If you are pregnant, breast-feeding, or trying to get pregnant, do not use any medicines unless your doctor tells you to. Some medicines can harm your baby. This includes prescription and over-the-counter medicines, vitamins, herbs, and supplements. And make sure that all your doctors know that you are pregnant, breast-feeding, or planning to get pregnant.


Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments. And call your doctor if you are having problems. It’s also a good idea to know your test results and keep a list of the medicines you take.


Last Revised: August 23, 2013

Author: Healthwise Staff

Medical Review: Rakesh K. Pai, MD, FACC – Cardiology, Electrophysiology & Anne C. Poinier, MD – Internal Medicine & Stephen Fort, MD, MRCP, FRCPC – Interventional Cardiology