Heart attack and ischemic stroke (“strokes”) occur when blockages in the blood vessels that supply the heart or brain cut off blood supply long enough to damage parts of these organs. Aspirin decreases the chances of a heart attack or stroke in patients who have had heart attacks or strokes, and newer evidence suggests that aspirin is beneficial in certain persons who have not had a heart attack or stroke. Aspirin can cause uncommon but serious complications, such as bleeding in the digestive tract or brain. In 2002, the USPSTF recommended that adults who have risk factors for heart attack but have not yet had a heart attack discuss the benefits and harms of aspirin to prevent heart attacks with their doctors. The benefits of aspirin were likely to outweigh the harms for patients whose chances of having a heart attack in the next 5 years were at least 3 of 100 (3%). However, these recommendations were based on data mostly from men. The USPSTF wanted to update them.