The purpose of the study was to investigate the effect of low doses of dopamine in children. Fourteen cases were studied after open heart surgery. Cardiac output and renal parameters were determined under baseline conditions and under continuous infusion of dopamine 2.5 and 5 micrograms/kg/min. During the control period cardiac index was 2.62 +/- 0.19 L/min/m2, renal plasma flow was decreased at 269 +/- 41 mL/min/1.73 m2, GFR was 86.6 +/- 9.2 mL/min/1.73 m2, and filtration fraction was elevated at 37.1 +/- 1.9%. Plasma concentration of aldosterone correlated with the filtration fraction. At 5 micrograms/kg/min dopamine increased significantly cardiac output, renal plasma flow, and to a lesser extent GFR, thus decreasing the filtration fraction. At 2.5 micrograms/kg/min dopamine, increased renal plasma flow only in patients older than 5 y and had no effect on the other parameters. The increase of cardiac output in response to dopamine was abolished by propranolol pretreatment. By contrast, the hemodynamic renal response to dopamine was not altered by beta-blockade. These results indicate that 5 micrograms/kg/min of dopamine could prevent renal failure after open heart surgery in children by increasing renal blood flow and attenuating renal compensatory mechanisms.