In a double blind crossover five-week trial with a randomized onset in 12 patients with normal blood pressure, stable angina pectoris and more severe left ventricular dysfunction (ejection fraction less than or equal to 40%) the effect of placebo nifedipine and diltiazem on left ventricular function and tolerance of exercise was compared. The investigation was done by means of echocardiography after a load with stimulation of the heart by an oesophageal electrode. As compared with placebo, only diltiazem retarded significantly the period before development of stenocardia on stimulation of the heart. There was no significant difference between nifedipine and diltiazem as regards the effect exerted on the ejection fraction and time which elapsed after stimulation before stenocardia developed. The authors observed an unequal response of patients to the administration of nifedipine and diltiazem (some patients had less favourable findings, although they were not subjectively aware of this deterioration). Therefore these drugs must be administered to patients with angina pectoris and more severe left ventricular dysfunction with care and only if other drugs (nitrates or angiotensin convertase inhibitors) do not eliminate ischaemia and pain.