We studied the acute effects of nifedipine on left ventricular function and haemodynamics at constant heart rate in patients on beta-blocker therapy. Nifedipine significantly depressed left ventricular peak dP/dt and peak dP/dt x P-1. Nifedipine also significantly reduced systemic vascular resistance: this was associated with decreased systolic blood pressure and increased left ventricular stroke output, with slight non-significant increases of ejection fraction and mean circumferential shortening velocity. There was no change in left ventricular end-diastolic pressure. This clinical study shows that nifedipine increases cardiac output in association with arterial dilatation despite evidence for a negative inotropic effect. Such intrinsic negative inotropic effects would normally be masked by compensatory sympathetic activity.