The phosphodiesterase inhibitor CI-930 hydrochloride exerts a positive inotropic and vasodilator effect in experimental animals. The acute hemodynamic and hormonal effects of intravenous CI-930 were studied in 9 patients with severe congestive heart failure. At 60 minutes of drug infusion, there was an increase in cardiac index (2.7 +/- 0.9 vs 2.0 +/- 0.7 liters/min/m2, p less than 0.01) and positive dP/dt (1,390 +/- 470 vs 1,100 +/- 300 mm Hg/s, p less than 0.02). Additionally, there were decreases in mean systemic arterial (78 +/- 16 vs 86 +/- 15 mm Hg, p less than 0.01), mean right atrial (5 +/- 3 vs 9 +/- 4 mm Hg, p less than 0.02), mean pulmonary arterial (27 +/- 11 vs 37 +/- 9 mm Hg, p less than 0.01) and LV end-diastolic (19 +/- 8 vs 28 +/- 6 mm Hg, p less than 0.01) pressures. Heart rate did not change (97 +/- 17 vs 97 +/- 22 beats/min). The inotropic response correlated significantly (r = 0.70, p less than 0.05) with the dose of CI-930. Plasma renin activity did not change significantly (from 16 +/- 9 to 23 +/- 15 ng/ml/hour), nor did plasma norepinephrine or arginine vasopressin levels. The plasma atrial natriuretic peptide level decreased (from 153 +/- 97 to 83 +/- 35 pg/ml, p less than 0.02). These findings suggest that intravenous CI-930 hydrochloride is a useful therapeutic agent in congestive heart failure and that its use does not appear to further activate potentially deleterious hormonal systems.