The influence of dopamine (7 micrograms/kg b.w./min) and of combined high-dose insulin (7 IU/kg) and dopamine on the relationship between haemodynamic performance and myocardial oxygen consumption was studied 4-6 hours after aortocoronary bypass surgery. The ten patients in the 'dopamine' group and the nine in the 'insulin-dopamine' group responded equally to dopamine alone. In a second study period the cardiac output was increased 41.8 +/- 4.7% by insulin-dopamine and 25.9 +/- 6.7% by dopamine alone (p less than 0.05). As the heart-rate response was similar in both groups, the difference was mainly due to greater response of stroke volume in the insulin-dopamine group. Systemic vascular resistance decreased 27.4 +/- 5.1% in the insulin-dopamine group but was unchanged in the dopamine group (p less than 0.05). Myocardial oxygen consumption increased 70.7 +/- 15.6% in the dopamine group and 78.8 +/- 18.4% in the insulin-dopamine group (NS). The addition of high-dose insulin to dopamine thus improved the haemodynamic efficacy of dopamine without further increasing myocardial oxygen expenditure.