Nifedipine, a potent coronary vasodilator, was administered in a single sublingual dose of 20 mg to eight patients with mild to moderate congestive heart failure. Nifedipine produced a slight increase in heart rate (mean +/- standard error of the mean 73.3 +/- 3.2 versus 80.9 +/- 2.1 beats/min, p < 0.025) and an increase in cardiac index (from a control value of 3.51 +/- 0.22 to 4.06 +/- 0.31 liters/min per m2, p < 0.01). Arterial blood pressure decreased from 112.9 +/- 6.2/67.7 +/- 4.2 (mean 84.9 +/- 4.0) to 100.8 +/- 4.4/56.4 +/- 11.0 (mean 76.1 +/- 4.3) mm Hg (p < 0.01) and total systemic vascular resistance also decreased from a control value of 15.6 +/- 1.0 to 12.4 +/- 0.8 units (p < 0.01) after administration of nifedipine. These data suggest that nifedipine may be useful for vasodilation in congestive heart failure.