Eighteen patients with severe unstable heart failure who presented with hemodynamic deterioration after withdrawal of i.v. dopamine were treated with high doses of ibopamine (100 mg eight times a day, orally) in association with digitalis, diuretic, and vasodilator therapy. Ibopamine, used at these dosages, could effectively substitute for the i.v. infusion of dopamine in 15 of the 18 studied patients. Each patient was studied by right heart Swan-Ganz catheterization and two-dimensional echocardiography before and during ibopamine infusion, after dopamine withdrawal, and after acute ibopamine administration; measurements were then made after 3 months of chronic ibopamine treatment (100 mg eight times a day). Blood samples for plasma dopamine and epinine concentrations were obtained at the time of the hemodynamic measurements. Both drugs did not induce any significant change in arterial pressure whereas heart rate was slightly reduced after dopamine and chronic ibopamine. Cardiac index and stroke volume index were significantly increased by dopamine (from 1.81 to 2.24 L/min/m2 and from 20.3 +/- 6.5 to 27.7 +/- 8.1 ml/beat/m2) and acute and chronic ibopamine (from 1.80 to 2.15 and 2.23 L/min/m2 and from 22.4 +/- 6.8 to 28.2 +/- 7.5 and 30.3 +/- 7.0 ml/beat/m2, respectively); these changes were attended by a decrease in systemic vascular resistance; pulmonary pressures were not significantly modified. No significant change of the echocardiographic parameters was noted. During dopamine infusion, mean dopamine plasma concentrations were 211.8 +/- 32.4 pmol/ml; after acute and repeated administration of ibopamine, free epinine plasma concentrations averaged 45.1 +/- 14.5 and 62.2 +/- 12.7 pmol/ml, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)