Timolol treatment after myocardial infarction is generally related to a significant reduction in both mortality and reinfarction compared with placebo. Retrospective analyses of the timolol study are performed on subgroups of patients with a high placebo mortality. The present study shows that these patients are target groups for secondary prevention, as they benefit most from timolol treatment after myocardial infarction. In patients 65-75 years of age, the number of cardiac deaths and reinfarctions prevented by timolol treatment is twice as high as that of patients below 65 years of age. Timolol treatment is well tolerated in the older age group and the contraindications for timolol treatment are independent of age up to 75 years. The reduction in mortality and reinfarction is independent of heart size at baseline. However, in patients with cardiomegaly and compensated heart failure on treatment with digitalis and diuretics, timolol treatment may be of special importance because of the very high incidence of cardiac death in this group of patients. In patients with compensated heart failure on treatment with digitalis and diuretics, timolol treatment does not precipitate heart failure. Patients with stable diabetes mellitus basically behave like nondiabetic patients regarding inclusion rate, side effects, and timolol-related reduction in mortality and reinfarction. Decisions concerning secondary prevention with timolol should be independent of preinfarction and postinfarction angina. In conclusion, 70-80% of all the patients below 75 years of age surviving myocardial infarction, without contraindication to beta-blocker treatment, can be treated with timolol 10 mg twice daily to reduce mortality and reinfarction. In contrast to previous routines, secondary prevention with beta blockers should be especially directed to high-risk patients.