The efficacy of acute haemodynamic support with intravenous enoximone (2 × bolus 0.5 mg/kg; infusion 5.0 µg/kg/min) versus dopamine (3.0–4.0 µg/kg/min), over an 18-hour period, was investigated in patients to be weaned from cardiopulmonary bypass (placebo-controlled trial). Under steady-state conditions, enoximone produced a substantial increase in cardiac index (20.6 ± 1.7%), but no change in heart rate. The improvement in cardiac index with time until constant values were reached (6 h) was not directly paralleled by the plasma concentration of enoximone. Pharmacodynamically relevant concentrations were already present after 1 h of infusion (480 ± 68 ng/ml) and comparable with the value determined after 6 h (442 ± 37 ng/ml). After 18 h of infusion, plasma concentration had reached 742 ± 47 ng/ml without a further improvement in cardiac function. The augmentation of stroke volume index (23.3 ± 2.5%) occurred concomitantly with a decrease in systemic vascular resistance (-23.1 ± 0.6%), obviously due to a decrease in diastolic arterial pressure (-12.0 ± 3.8%). The pulmonary capillary wedge pressure remained unaffected. There was only a slight decrease in pulmonary vascular resistance (-9.3 ± 3.2%). During both enoximone infusion and dopamine infusion, right atrial pressure increased (10.0 ± 3.1 and 9.0 ± 1.8%, respectively), in contrast to the untreated control group. This is contradictory to the drugs’ described effect in patients suffering from congestive heart failure. At a concentration which would not normally cause cardiac acceleration, dopamine provided minor haemodynamic support in the period after cardiopulmonary bypass. A small increase in cardiac index (5.9 ± 2.2%) was accompanied by a slight decrease in systemic (-4.2 ± 3.2%) and pulmonary ( 11.4 ± 2.4%) vascular resistances. The results indicate that enoximone produced beneficial haemodynamic effects in the period following cardiopulmonary bypass. Both inotropic and vasodilatory effects appeared to be manageable.