Twenty patients (5 females, 15 males) with severe heart failure (NYHA IV), due to coronary artery disease in 14, and congestive cardiomyopathy in 6, received an intravenous bolus of the calcium blocker nisoldipine 0.2 mg followed by a continuous infusion of 0.2 micrograms.kg-1.min-1. Haemodynamic measurements were performed at baseline and after 30 min. The mean arterial pressure fell from 91 to 73 mmHg, pulmonary capillary wedge pressure from 31 to 26 mm Hg and systemic vascular resistance from 1695 to 1040 dyn.s.cm-5. The cardiac index (2.2 to 2.71.min-1.m-2, and stroke volume index (25 to 33 ml.m-2) were markedly increased. There was no reflex tachycardia as the heart rate dropped from 92 to 85 beats.min-1. Plasma renin activity and norepinephrine concentration did not change significantly. The findings indicate that nisoldipine acts as a strong vasodilator and that it has a beneficial acute haemodynamic effect in patients with severe left heart failure irrespective of its aetiology.