Intracardiac obstruction to the systemic circulation can develop in patients with many forms of congenital heart disease. When transposition of the great arteries accompanies tricuspid atresia, narrowing of the ventricular septal defect (VSD) leads to subaortic stenosis. In a similar fashion, a restrictive bulboventricular foramen compromises systemic arterial outflow in patients who have single left ventricle with subaortic outflow chamber. The same effect can be seen in VSD closure in mitral atresia with normally related great vessels. Although some forms of single ventricle can be treated by ventricular septation, the modified Fontan procedure can be more generally applied to this entity. Pulmonary vascular resistance must be low, however, which excludes the application of the Fontan principle in infants. While pulmonary artery banding may protect the lungs from the development of excessive pulmonary vascular resistance, it may also accelerate the development of subaortic obstruction. We have successfully applied the Norwood operation, as described for hypoplastic left heart syndrome, to palliate subaortic stenosis due to restrictive VSD in 3 infants with single ventricle or atrioventricular valve atresia. Consideration should be given to a primary Norwood procedure in infants with single ventricle in whom subaortic stenosis is likely to develop. Patients who do receive pulmonary artery bands should be followed closely for the development of subaortic stenosis and should undergo an early, physiologically corrective operation if it occurs.