How does low-dose aspirin prevent a heart attack or stroke?

Holly S. Andersen, MD
Cardiology (Cardiovascular Disease)
Low-dose aspirin has been shown to prevent heart attack and stroke because it interferes with blood clotting. In this video, cardiologist Holly Andersen, MD, explains how aspirin inhibits platelet function, which can avert a heart attack or stroke. 
Aspirin prevents platelets in your blood from being bound together into a patch that the body uses to form clots. This is the beginning of the process to stop bleeding -- for example, when you cut your skin. However, clots can form in the bloodstream, too, in which case, they are at risk of getting stuck in a blood vessel, including in the heart or brain. Clots there could cause a heart attack or stroke, respectively. However, because of this same effect, taking aspirin daily, even low doses, can increase the risk of bleeding events, especially along the digestive tract. Therefore, the recommendation is that adult men ages 45 to 79 years at increased risk of heart attack, or adult women ages 55 to 79 years at increased risk of stroke, should take a daily aspirin in the absence of other reasons against doing so. You should talk to your doctor about whether he or she thinks this is appropriate for you.

Low-dose aspirin works to prevent heart attack and stroke by acting as a blood thinner, reducing the clumping of platelets in the blood and slowing the blood's ability to clot. By lowering the risk of blood clot formation, low-dose aspirin reduces the risk of heart attack and stroke, as these occur when a blood clot blocks a narrowed artery and cuts off flow of oxygenated blood to the heart or brain.

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