Investigations were performed to determine whether prostaglandin E1 (PGE1) would cause a favorable change in pulmonary hemodynamics in pediatric patients with congenital heart disease and elevated pulmonary vascular resistance. Twenty-seven patients (ages 0.5 months to 19 years) were studied. PGE1 caused a significant decrease in mean pulmonary artery pressure with 0.05 microgram/kg/min and 0.1 microgram/kg/min infusions (p = .0004). There were significant increases in pulmonary blood flow (p = .0007), and decreases in pulmonary vascular resistance (p = .0001); changes in systemic pressure, resistance, oxygen consumption, and heart rate were minimal. Twenty-three patients underwent heart surgery after catheterization, nineteen of these survived. The four nonsurvivors had higher initial pulmonary resistance (PVR) and less decline in PVR with PGE1 than survivors. This study shows that PGE1 is an effective pulmonary vasodilator in patients with congenital heart disease and elevated pulmonary vascular resistance.