In a double-blind, randomized, placebo controlled trial 74 patients surviving a myocardial infarction (MI) were stress tested three and twelve months following MI. Thirty-eight patients received the beta blocking agent timolol and 36 patients received placebo. There was no significant difference in the mean total exercise capacity of the two groups. Most of the patients treated with timolol discontinued the exercise test because of exhaustion, but the placebo treated patients usually stopped the test because of chest pain, exhaustion or a fall in blood pressure. Patients treated with timolol had significantly less increase in heart rate, systolic blood pressure and rate-pressure product during exercise compared to placebo. We conclude that beta-blockade with timolol after MI does not affect work capacity, but timolol-treated patients perform the same work with a lower rate-pressure product.