Abstract: Objective: To discuss the indication,technique and preoperative management of low weight infants with critical congenital heart defects.Methods: The clinical data of 32 infants under 12 kg undergoing cardiac operation from May 1999 to October 2004 in our hospital were reviewed retrospectively.The symptoms included ventricular septal defect with pulmonary hypertension,tetralogy of Fallot,atrial septal defect with pulmonary stenosis and patent ductus arteriosus.Results: Two cases died after operation and the hospital mortality was 6.3%.The average duration of mechanical ventilation was (18±8.6) hours and the average ICU stay was (4.5±1.5) days.The follow-up lasted for 2 to 24 months.The cardiac function of the patients improved greatly and the growth approximated the normal.Conclusions: With the development of pediatric heart surgery,cardiac operation on infants with low weight and critical congenital heart defects is safe and feasible.