The acute hemodynamic effects of intravenous prostacyclin (PGI2), in doses of 22 +/- 11 ng/kg per min were studied in nine patients with severe congestive heart failure refractory to digitalis and diuretic drugs. After prostacyclin infusion, mean (+/- standard deviation) pulmonary capillary wedge pressure decreased from 21.0 +/- 7.9 to 15.0 +/- 6.6 mm Hg (p less than 0.001), mean arterial pressure from 98.9 +/- 12.8 to 76.2 +/- 7.0 mm Hg (p less than 0.001), systemic vascular resistance from 2,574 +/- 384 to 1,368 +/- 283 dynes s cm-5 (p less than 0.001), pulmonary vascular resistance from 1,008 +/- 451 to 443 +/- 135 dynes s cm-5 (p less than 0.001) and pulmonary arteriolar resistance from 330 +/- 111 to 189 +/- 73 dynes s cm-5 (p less than 0.001). Heart rate increased from 78 +/- 21 to 82 +/- 24 beats/min (p = not significant [NS]), cardiac index from 2.0 +/- 0.37 to 3.2 +/- 0.59 liters/min per m2 (p less than 0.001) and stroke index from 27.6 +/- 8.69 to 42.0 +/- 0.62 cc/m2 (p less than 0.001). With prostacyclin, moreover, coldness of the limbs and face disappeared, and patients felt warmth and mild flushing of the face. After prostacyclin, plasma norepinephrine levels, renin activity and aldosterone concentrations rose from 824 +/- 375 to 880 +/- 468 pg/ml (NS), 0.68 +/- 1.36 to 0.95 +/- 1.21 ng/ml per h (NS), and 6.64 +/- 2.50 to 6.38 +/- 2.88 ng/dl (NS), respectively, while plasma epinephrine increased from 140 +/- 80 to 250 +/- 154 pg/ml (p less than 0.025).