United States guidelines suggest any aspirin dose between 81 mg and 325 mg daily for patients with coronary heart disease, while European guidelines that recommend 81 mg daily are mainly based on observational data and expert opinion. To help determine the best aspirin dose for this patient population, investigators randomly assigned patients with established heart disease to 81 mg or 325 mg of aspirin daily. After a mean follow-up of 26 months, a composite of all-cause death, myocardial infarction, or stroke occurred in 7.28% of those assigned to 81 mg and 7.51% of those assigned to 325 mg. Hospitalization for major bleeding with an associated blood transfusion occurred in 0.63% of the 81-mg group and 0.60% of the 325-mg group. Dose switching occurred in 41.6% of those assigned to 325 mg, compared with 7.1% of those assigned to 81 mg, while treatment discontinuation occurred in 11.1% and 7.0%, respectively.