It is sort of a misnomer to consider aspirin as a blood thinner . It is an antiplatelet agent. The platelets are part of the healing process and become sticky when activated by chemicals found in the epithelium(which are normally not active unless an injury happens) The platelets form an initial microscopic mesh over a wound that initiates homeostasis (bleeding to stop). Aspirin is also an anti-inflamatory. The process for a heart attack is usually started with inflamation of the plaques inside the artery. This is followed by a rupture of a plaque. The subsequent clotting and embolism from the rupture is usually the precipitant that completely blocks the artery and causes a sudden cardiac event. Aspirin accomplishes two main functions - it is an anti-inflammatory and helps to prevent the plaque rupture in the first place. If a plaque does rupture it inhibits the platelets from getting sticky and begin forming a clot. Therefore aspirin does not prevent heart disease but it will help prevent acute events from happening. If they do happen then it will reduce the severity of the event by reducing the clotting action inside the artery, thereby reducing the blockage inside the artery that is preventing blood to flow to the heart muscle. Studies show that for most patients a low dose aspirin (81mg) is adequate accomplish the anti-inflamatory process without causing undo adverse affects like stomach lining irritation/bleeding. With acute chest pain it is recommended that you CHEW a full aspirin (325mg) while waiting for the ambulance to arrive or enroute to the ER - even if you take 81mg daily. Good luck.