81 mg po daily

For individuals with known cardiac disease.

Useful reference:
If individuals have no known cardiac disease, you must give 254 patients daily aspirin for 7 years to prevent 1 cardiovascular event. The risk of a major bleed in this group has approximately the same rate.

Berger JS, Lala A, Krantz MJ, Baker GS, Hiatt WR. Aspirin for the prevention of cardiovascular events in patients without clinical cardiovascular disease: A meta-analysis of randomized trials. Am Heart J 2011;162(1):115-124.e2.