We compared the acute hemodynamic effects of intravenous nitroprusside (NTP), a pure vasodilator, to those of intravenous MDL-17,043 (MDL), a phosphodiesterase inhibitor with inotropic and vasodilator effects, in 12 patients with chronic refractory congestive heart failure (CHF). Intravenous NTP was infused and titrated to achieve optimal hemodynamic effects, whereas MDL was given intravenously in 0.5 mg/kg increments every 10 to 15 minutes until no further increase occurred in cardiac output or until a maximum cumulative dose of 4.5 mg/kg had been given. Both NTP and MDL reduced pulmonary capillary wedge pressure (27 +/- 5 to 15 +/- 6 and 29 +/- 3 to 15 +/- 7 mm Hg, respectively; both p less than 0.0001), systemic vascular resistance (2173 +/- 1137 to 1118 +/- 306 and 1805 +/- 425 to 956 +/- 235 dynes-sec-cm-5, respectively; both p less than 0.0002), mean arterial pressure (85 +/- 18 to 69 +/- 14 and 83 +/- 15 to 75 +/- 16 mm Hg respectively; both p less than 0.05), and increased cardiac index (1.7 +/- 0.4 to 2.6 +/- 0.4 and 1.8 +/- 0.2 to 3.3 +/- 0.5 L/minute/m2, respectively; both p less than 0.05) without an overall significant change in heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)