Aspirin in the primary prevention of angina pectoris in a randomized trial of United States physicians. PURPOSE: The objective of this study was to examine the effect of low-dose aspirin (325 mg on alternate days) on the primary prevention of angina pectoris in the United States Physicians' Health Study. Despite a postulated role of platelets in atherogenesis and myocardial ischemia, the effect of chronic platelet inhibition on the development of clinical angina pectoris is unknown. SUBJECTS AND METHODS: The Physicians' Health Study is a randomized, double-blind, placebo-controlled trial among 22,071 male physicians aged 40 to 84 years, free from previous myocardial infarction, stroke, and transient cerebral ischemia at entry, and followed for an average of 60.2 months. The 21,738 physicians who were also free from angina pectoris at baseline constituted the study population for the present analyses. RESULTS: During 106,652 person-years of follow-up, 331 patients with confirmed angina pectoris were diagnosed, 194 of whom underwent a coronary revascularization procedure (coronary artery bypass graft surgery or coronary angioplasty). As compared to participants assigned placebo, the relative risk of confirmed angina pectoris in the aspirin group was 1.10 (95% confidence interval [CI], 0.88 to 1.38). For coronary revascularization, the relative risk was 1.19 (95% CI, 0.88 to 1.59). After simultaneous control for other coronary risk factors in a proportional-hazards model, these relative risks remained near unity at 1.07 (95% CI, 0.84 to 1.36) and 1.11 (95% CI, 0.81 to 1.52), respectively. When the risks of angina pectoris were examined according to year of randomization in the trial, there was no pattern of increasing benefit with longer duration of treatment. CONCLUSION: These randomized trial data indicate that chronic platelet inhibition with low-dose aspirin for an average duration of 60.2 months does not reduce the incidence of angina pectoris. 