We administered 150 mg of ibopamine orally to 10 patients suffering from idiopathic congestive cardiomyopathy. Hemodynamic function was evaluated by right heart catheterization and by measurement of cardiac output with the thermodilution technique. Ibopamine caused no significant change in heart rate or mean arterial pressure. Cardiac index, stroke volume index, and left ventricular work index all increased significantly by about 30%. Mean pulmonary arterial pressure decreased by about 30%, and systemic vascular resistance decreased by about 20%. The effects peaked at about 3 h and lasted 5-7 h. No side effects were noted. These findings with invasive techniques confirm those of others using noninvasive techniques, and suggest that ibopamine may be useful in the treatment of congestive heart failure.