Résumé : Objective and methods: From September 1990 to February 1997, 23 consecutive critically ill infants (12 males, 11 females) weighing 2500 g or less underwent cardiac surgery necessitating extracorporeal circulation (ECC). A retrospective study was carried out to evaluate short- and intermediate-term outcome. Mean weight at operation was 2265 g (range 1750- 2500 g). Mean age at operation was 24 days. The indications for surgery were transposition of the great arteries (TGA; 7), ventricular septal defect (VSD; 4), aortic stenosis (AS; 3), univentricular heart (UVH; 2), tetralogy of Fallot (TOF; 2), interrupted aortic arch (IAA; 2), atrial septal defect (ASD; 1), atrioventicular septal defect (AVSD; 1) and total abnormal pulmonary venous return (TAPVR; 1). All patients were in NYHA class IV; 17 patients (74%) were intubated pre-operatively. Results: The mean aortic cross-clamping time was 40 min. Twelve patients required deep hypothermia (<20°C) with total circulatory arrest (mean duration 19 min). All patients were successfully weaned from extracorporeal circulation (ECC). Five patients left the operating room with an open sternum (mean duration before closure: 3.5 days). Mean duration of artificial ventilation was 10.6 days; of inotropic support 6.7 days and of intensive care stay 17.8 days. Severe complications were observed in 19 patients (83%): cardiac failure requiring high inotropic support (13), sepsis (7), and acute renal insufficiency (5). One patient needed a ventricular assist device. Five patients (22%) died in the intensive care unit (ICU): 2 AS with fibroelastosis, 2 IAA with VSD, and 1 UVH with pulmonary atresia. At discharge from the ICU, 7 patients were receiving no treatment. Mean duration of follow-up was 32 months (range 2-80 months). We had 2 reoperations: 1 for right ventricular outflow tract obstruction 1 year after a switch operation and 1 for mitral valve replacement 1 year after total abnormal pulmonary venous return repair (death 30 days post mitral valve replacement). Survival at I year was 73%. At the last clinical examination 16 patients were in NYHA class I. Conclusion: Despite the severity of pre-operative cardiac disease, early surgical repair with ECC in infants weighing 2500 g or less is feasible with tolerable mortality yet with significant early morbidity.