The hemodynamic effects of combined administration of ibopamine (Ib) (150 mg orally) with nitroprusside (NP) (50-150 micrograms/min intravenously) were compared with those of NP alone in 17 patients with severe congestive heart failure due to coronary artery disease (7 patients) or idiopathic cardiomyopathy (10 patients). Hemodynamic measurements were obtained using a Swan-Ganz thermodilution catheter and a bedside thermodilution cardiac output computer. Nitroprusside alone produced a significant decrease (-12.4%) in mean arterial pressure, mean pulmonary arterial pressure (-28.3%), and systemic vascular resistance (-22.6%), and a significant increase in stroke volume index (23.1%). The administration of combined NP and Ib produced a further significant increase of stroke volume index (20.1%) with a concomitant and significant reduction of systemic vascular resistance (-19.4%); heart rate, mean systemic and pulmonary arterial pressures did not change significantly from the values observed with NP alone. Moreover, stroke work index, although not significantly modified with the vasodilator alone, was significantly increased over control values with NP + Ib association. Although NP alone induced similar effects in both the ischemic and idiopathic cardiomyopathies, the association of Ib gave a more favorable, though not significant, hemodynamic response in the subjects with primitive cardiomyopathy than in the ischemic ones. Thus, the association of Ib to NP therapy, in patients with congestive heart failure, further increases stroke volume index and stroke work index with a concomitant reduction of systemic vascular resistance, without any significant change in mean systemic and pulmonary arterial pressures, or heart rate. These results point out the possibility of associating Ib with other orally active vasodilators in the chronic treatment of congestive heart failure.