Infusion of prostaglandin E1 into the main pulmonary artery of an infant with interruption of the aortic arch and a closing ductus arteriosus resulted in dilation of the ductus arteriosus and improved systemic perfusion. Treatment with prostaglandin E1 is recommended for infants with interruption of the aortic arch, critical coarctation of the aorta, and other lesions in which systemic perfusion is limited by a restrictive ductus arteriosus.