Aspirin is on the of the oldest used compounds in the doctors bag. Its uses include:

Painkiller: 300mg tablets

Vascular disease: 75-300mg tablet

It is a platelet inhibitor. The platelets are a key component in the blood coagulation chain and are responsible, in a large part, for the  clots in heart attacks. Blocking this, via Aspirin, has been proven to be beneficial in a large number of clinical scenarios, most notably, in patients who have had myocardial infarction (heart attack), unstable angina, chronic stable angina; they have all been proven to be beneficial.

Atrial Fibrilliation:

The benefit of Aspirin in atrial fibrillation is less than that of Warfarin. It is now not recommended.

The downside of the regular use of Aspirin is that a certain proportion of patients are unable to take Aspirin due to gastric intolerance and the formation either of a gastritis, or more significantly, of gastric ulcers and bleeding of the stomach lining. We will evaluate your risk of developing this carefully before initiating Aspirin and may well prescribe another drug to protect the lining of the stomach during the duration of your Aspirin therapy.