Aspirin low-dose works as a blood thinner, reducing the clumping of platelets. This slows the blood's ability to clot. During a heart attack a blood clot forms in a narrowed artery, cutting off the flow of blood to the heart. Taking aspirin low-dose helps to keep blood from clotting further and making the blockage worse. If you are experiencing a heart attack, immediately call 911 and follow up with aspirin low-dose. Do not use a low-dose of aspirin as a substitute for urgent medical attention.