Aspirin, a blood thinner, is useful for heart attack, which develops due to a clot in an artery that supplies the heart with blood. Stroke, on the other hand, may results from either clotting in, or bleeding from, one of the brain arteries. Hypothetically, Aspirin would be useful in case of clotting, but harmful with bleeding. Since it is impossible without a CT scan to identify the underlying issue, aspirin should be avoided in stroke.