Despite widespread clinical application of propranolol (P) in angina pectoris, convincing evidence of its efficacy has been incomplete, thereby resulting in continued controversy. Its antianginal effectivess was investigated in 20 patients with documented coronary heart disease in a 44-wk study incorporating a prolonged 12-wk lead-in period, individualization of P dosage in a 6-wk dose-finding period, and a 24-wk doule-blind crossover phase. On double-blind placebo, patients had 10.5 +/- 2.1 anginal attacks and consumed 12.8 +/- 3.0 nitroglycerin tablets (NTG) each week compared to 6.6 +/- 1.5 anginal episodes (- 37%, p less than 0.001) and 8.0 +/- 1.7 NTG (-38%, p less than 0.001) when on P. No patient experienced more angina with P than with placebo. In addition, time to onset of chest pain during treadmill exercise was prolonged by P from 190 +/- 16 to 248 +/- 22 sec (+31%, p less than 0.02) and ST depression was reduced from 1.7 +/- 0.21 to 0.99 +/- 0.18 mm (-42%, p less than 0.05). There was correlation (r = 0.64 p less than 0.01) between per cent declines in anginal frequency and resting double product with P. Thus, propranolol favorably altered several indices of myocardial ischemia in severe coronary heart disease. This investigation clearly documents the clinical efficacy of optimal beta adrenergic blockade in coronary disease and provides objective justification for the judicious application of propranolol in treatment of angina pectoris.