Backgroud: There are well-known problems in the management of low weight neonates or infants with congenital heart defects. In the past, because of a perceived high risk of operations using cardiopulmonary bypass(CPB) in these patients, there was a tendency for staged palliation without the use of CPB. However, the recent trend has been toward early reparative surgery using CPB, with acceptable mortality and good long-term survival. Therefore we reviewed our results of the operations in infants weighing less than 3kg and considered the technical aspect of conducting the CPB including myocardial protection. Material and Method: Between Jan. 1995 and Jul. 1998, 28 infants weighing less than 3kg underwent open heart surgery for many cardiac anomalies with a mean body weight of 2.7kg(range; 1.9-3.0kg) and a mean age of 41days(range; 4-110days). Preoperative management in the intensive care unit was needed in 20 infants and preoperative ventilator support therapy in 11. Total correction was performed in 23 infants and the palliative procedure in 5. Total circulatory arrest was needed in 11 infants(39%). Result: There were seven hospital deaths(25%) caused by myocardial failure(n=3), surgical failure(n=2), multiorgan failure(n=1), and sudden death(n=1). The median duration of hospital stay and intensive care unit stay were 13days(range; 6-93days) and 6days(range; 2-77days) respectively. The follow-up was achieved in 21 patients and showed three cases of late mortality(15%) and a one-year survival rate of 62%. No neurologic complications such as clinical seizure and intracranial bleeding were noticed immediately after surgery and during follow-up. Conclusion: The early and late mortality rate of open heart surgery in our infants weighing less than 3 kg stood relatively high, but the improved outcomes are expected by means of the delicate conduct of cardiopulmonary bypass including myocardial protection as well as the adequate perioperative management. Also, the longer follow-up for the neurologic development and complications are needed in infants undergoing circulatory arrest and continuous low flow CPB.