The purpose of the study was to assess the relationship between left and right ventricular function measured at rest and maximal exercise capacity in patients with recent acute myocardial infarction (AMI). Forty-three male patients (Killip Class I, n = 36; Killip Class II, n = 7) with a wide range of left ventricular (LV) function and size underwent graded bicycle exercise testing less than 4 weeks after AMI (mean 21 days, 17-27). None of the patients had exercise limiting factors other than dyspnoea and fatigue. Left and right ventricular ejection fractions were determined by a radionuclide ventriculographic method which also allowed determination of absolute LV volumes and actual LV peak filling rate. LV ejection fraction had a weak association to estimated maximal oxygen uptake (VO2 max) (r = 0.37). No association was found between LV size, LV stroke volume, or LV peak filling rate and estimated VO2 max. Similarly, right ventricular ejection fraction showed no correlation to estimated VO2 max. Patients with well preserved LV function had a higher exercise induced increase in systolic blood pressure than patients with reduced LV function, but the increase in systolic blood pressure could not be used to estimate LV function with any reasonable accuracy. We conclude that the maximal exercise capacity of patients with recent AMI is virtually independent of their left and right ventricular function determined at rest, and that exercise testing and radionuclide ventriculography should be regarded as complementary procedures in the evaluation of patients with AMI.