The hemodynamic effects of a newly developed inotropic agent, amrinone (AMN) were studied and compared with those of dopamine (DA) and dobutamine (DB) in forty patients with pump failure due to acute myocardial infarction. Hemodynamic measurements were taken using a Swan-Ganz thermodilution catheter before and 5, 10, 15, 30, 60, 90 and 120 minutes after intravenous injection of AMN (1-2 mg/kg) for 3 minutes in eight patients, and also before and during drip infusion (3-7 micrograms/kg/min) of DA in fifteen patients and DB in seventeen patients. AMN showed maximal increases in CI, SVI and SWI, and maximal lowering in CVP and SVR 5 minutes after intravenous injection, while maximal lowering in PCWP occurred 10 minutes after injection. These significant hemodynamic changes lasted for 60 minutes after injection. Comparing the maximal hemodynamic effects occurring 5 minutes after injection of AMN with those of DA and DB, it was found that AMN increased CI to almost the same degree as DA, and lowered CVP and PCWP much more compared to DB. These results suggest that AMN possesses a dominant vasodilating effect in addition to its inotropic effect, which would greatly benefit the treatment of refractory heart failure; AMN are the characteristic cardiovascular hemodynamic effects of as if catecholamine and a vasodilator were combined.