The hemodynamic effects of nitroprusside and dopamine were studied in 28 children early after intracardiac repair. Children were placed in six groups, five according to their anatomic lesion and one made up of those who had postoperative pulmonary artery hypertension, to evaluate the possible differences in response of the pulmonary arterial vasculature to the drugs. Seven children had repair of an atrial septal defect; six, repair of tetralogy of Fallot; four, repair of ventricular septal defect; five, surgery for pulmonary stenosis; one, closure of a left ventricular to right atrial tunnel; and five, postoperative pulmonary artery hypertension. Dopamine was infused at 8 microgram/kg/min, and nitroprusside at 3 microgram/kg/min. With dopamine, the heart rate increased an average of 10% and the cardiac index 11%; both increases were statistically significant. Changes in systemic and pulmonary vascular resistance, however, were not. With nitroprusside, the heart rate increased an average of 9% and the cardiac index 5%, while there was a significant decrease in both systemic (-20%) and pulmonary (-27%) vascular resistance. With the combination of dopamine and nitroprusside, both the cardiac index (+13%) and heart rate (+20%) increased significantly while systemic vascular resistance fell an average of 23% from control, and the pulmonary vascular resistance decreased 21%. Drug response among all five anatomic subgroups tended to be similar. We conclude that an afterload-reducing agent, such as nitroprusside and an inotropic drug such as dopamine, may have potential clinical advantages when used together in children providing heart rate does not become excessive.