Why You Should Take Aspirin If You're Having a Heart Attack

Early Aspirin Use Can Reduce Blood Clot Size

Man holding asprin
David Sucsy/Getty Images

If you have ever had a heart attack, your doctor has probably told you to carry an aspirin or two with you at all times, and to chew and swallow one immediately if you ever think you might be having another heart attack. “While you are dialing 911,” she probably said, “chew and swallow an aspirin.” 

And if your doctor hasn’t told you to do this, he should have.

As it turns out, in the very earliest stages of a heart attack, in those critical minutes when part of your heart muscle is losing its blood supply, a simple aspirin can make a huge difference. It can mean the difference between a little heart damage and a lot of heart damage; it can mean the difference between living and dying.

Anyone who has had a heart attack in the past, or is known to be at risk for a heart attack in the future, should always carry a few aspirin with them, and chew and swallow one immediately if they experience significant chest pain, or any other signs of an acute heart attack.


Why Take an Aspirin While Waiting for the Paramedics

A heart attack, also called myocardial infarction, is usually a form of acute coronary syndrome (ACS). ACS is triggered by the rupture of a plaque within a coronary artery. This plaque rupture causes a thrombus (blood clot) to form within the artery, leading to a blockage. The portion of the heart muscle being supplied by the artery then begins to die. The death of heart muscle is what defines a myocardial infarction.

What this means is that, at the time you are having a heart attack, a big part of the problem is the growth of a blood clot within the affected artery. Formation of this blood clot depends to a large extent on the blood platelets, which are tiny blood cells whose job is to participate in blood clotting.

Why Aspirin?

It turns out that aspirin—even in small doses—can rapidly and powerfully inhibit the activity of the platelets, and therefore can inhibit the growth of the blood clot. Inhibiting the growth of the blood clot is critical if you're having a heart attack since maintaining at least some blood flow through the coronary artery can keep heart muscle cells from dying.

Large randomized clinical trials have shown that if aspirin is used soon after the onset of an acute heart attack, the mortality rate after five weeks is reduced by as much as 23 percent.

Just as importantly, clinical trials have also strongly suggested that the early administration of aspirin can substantially reduce the size of the myocardial infarction, or convert a heart attack to unstable angina, or convert an ST-segment elevation myocardial infarction (STEMI) to a non-ST segment elevation myocardial infarction (NSTEMI). All of these benefits can greatly diminish the amount of heart damage you end up with, and (more importantly) can greatly diminish (or even eliminate) the long-term disabilities you’ll be dealing with.

This is why chewing and swallowing an aspirin is usually one of the first things you will be asked to do when you arrive in the emergency room with a suspected MI — if you have not done so already.

But time is of the essence—minutes count. So if you think you might be having a heart attack, most experts now advise patients not to wait until they get medical help—chew and swallow an aspirin as soon as you are concerned enough to call the paramedics.

By doing this you can begin treating the heart attack immediately, even before the paramedics arrive.

How Much, What Type, and How To Take It

The current recommendation for people who may be having a heart attack is to chew and swallow one non-coated adult aspirin (325 mg) as soon as possible. Chewing or crushing the aspirin gets it into your bloodstream more quickly—within four to five minutes—and researchers have measured a significant effect on platelets within that short period of time.

Swallowing a whole aspirin with water, as you normally would, takes 10 to 12 minutes to achieve the same effect. This time difference may seem small, but, once again, minutes count when your heart is at risk.

A Word From Verywell

Aspirin is effective in reducing the blood clots that are blocking a coronary artery during an acute heart attack. Anyone who has already had a heart attack, or who has an increased risk of having one in the future, should always carry a few non-coated adult aspirins with them. At the first sign of a heart attack they should chew and swallow one while they’re dialing 911.

Was this page helpful?

Article Sources

  • Berger JS, Stebbins A, Granger CB et al. Initial Aspirin Dose and Outcome Amongst ST-Elevation Myocardial Infarction Patients Treated With Fibrinolytic Therapy. Circulation 2008;117:192–9.

  • Randomised trial of intravenous streptokinase, oral aspirin, both, or neither among 17,187 cases of suspected acute myocardial infarction: ISIS-2. ISIS-2 (Second International Study of Infarct Survival) Collaborative Group. Lancet 1988; 2:349.
  • Wright RS, Anderson JL, Adams CD, et al. 2011 ACCF/AHA Focused Update of the Guidelines for the Management of Patients With Unstable Angina/ Non-ST-Elevation Myocardial Infarction (Updating the 2007 Guideline): a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2011; 123:2022.