The study group consisted of 8 men with congestive heart failure. They ranged in age from 33 do 63 years (mean 48). Three patients were in class III NYHA, five in class IV. Idiopathic cardiomyopathy was diagnosed in 6 patients, one individual displayed ischemic heart disease and one patient was after mitral and aortic-valve replacement despite a normally functioning prosthetic valve. L-dopa was given orally beginning with 250 mg every six hours until a total daily dose of 4.0 g was achieved with no side effects (patients additionally received 50 mg of pyridoxine hydrochloride). Afterwards L-dopa was withheld for 24-36 hours. Having completed this washout period, patients underwent right heart catheterization, with placement of a balloon-tipped thermodilution catheter in a pulmonary artery, so that balloon inflation allowed recording of the pulmonary capillary wedge pressure. Right atrial and pulmonary arterial pressures were monitored continuously. Systemic arterial pressure was measured by mercury manometer. Cardiac output was determined by the thermodilution technique. Rest and effort hemodynamic measurements were repeated before and one, three hours after administration of 1-dopa. The base-line hemodynamic values were consistent with the clinical presentation of severe congestive heart failure. The average cardiac index (CI-1/min/m2--rest--1.93; 25 Watt-3.1) and stroke volume index (SVI-m1/m2--rest--22.2; 25 Watt-32.0) were markedly lowered. Left ventricular filling pressure and pulmonary artery pressure were elevated. The systemic vascular resistance was significantly increased (SVR -j.W.--rest--22.7; 25 Watt-14.2). Administration of 1-dopa resulted in the increase in cardiac index and stroke volume index accompanied by a substantial reduction in systemic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)