Daily 500 mg doses of aspirin were shown to be sufficient to produce lasting (one year long) inhibition of platelet aggregation. Two matched samples of postmyocardial infarction patients were compared: 844 untreated controls and 570 patients treated with 500 mg aspirin daily for 1 year following myocardial infarction. In the treated sample, the incidence of recurrent myocardial infarction, including sudden death, dropped from 13.1 to 8.9%, coronary mortality, including sudden death, from 7.2 to 4.7%, sudden death rate, from 3.2 to 1.9%, and total mortality, from 9.3 to 6.6%, as compared to the untreated sample.