Surgical treatment of cardiac defects in infants born with extremely low weight is sometimes required during the neonatal period. Optimal timing of these operations has yet to be clarified. With this in mind, we reviewed our experience of surgical treatment for 29 infants born with extremely low weight between 1994 and 2001. The main surgical procedures were ligation of a patent arterial duct in 26, a Brock procedure in 2, and ligation of an aorto-pulmonary window in 1 infant. The age at operation ranged from 5 to 57 days, with a median of 30 days, and weighed from 506 to 902 g, with a median of 710 g. There were no deaths. For the 2 infants undergoing the Brock procedure, the reduced systemic blood flow also necessitated closure of the arterial duct. For almost all the 26 infants with a patent arterial duct, indomethacin was given as the initial therapy, but the duct had not closed completely. Increased symptomatology just before the operation due to reduced systemic blood flow, such as decreased cerebral blood flow, decreased urine output, and intestinal ischemia, mandated the earlier surgical ligation (r = −0.576, p = 0.004). The youngest infant needed an infusion of catecholamines perioperatively to maintain stable hemodynamic conditions (r = 0.554, p = 0.003). In 4 infants, including the youngest 2, steroids were administered intravenously just after the ligation. Our results suggest that reduced systemic blood flow is the main indication of surgical repair in infants born with extremely low weight. Even for one in whom the supply of pulmonary blood is dependent on the arterial duct, early reconstruction of the pulmonary arterial pathways, using the Brock procedure, followed by ligation of the duct, is required. Acute adrenal insufficiency should not be overlooked just after the surgery, particularly in the youngest patients.