From January 1983 to December 1992, 116 patients under 10Kg of body weight were underwent open heart surgery in National Medical Center.There were 64 males and 52 females, and their mean age was 14 2.6 months, ranged from 3 days to 38 months. Their mean body weight was 7.4$pm$1.2Kg, ranged from 2.4Kg to 10Kg which were less than 3 percentile of normal developmental pattern in 109 out of 116 cases.The composition of the patients was VSD[73 , TOF[18 , ASD[8 , ECD[5 , TGA[4 , PS[3 , TAPVC[2 , TA[1 , cardiac rhabdomyoma with ASD[1 , and Ebstein`s anomaly[1 . The overall surgical mortality was 17.2%.In acynotic group, 11 patients died among 91 patients and the mortality was 12.1%, in cyanotic group 9 patients died among 25 patients, the mortality was 36%.The surgical result of patients under 5Kg of body weight was worse than those over 5Kg of body weight. [56.2% versus 11% The surgical result in this period was improved year by year, but poor surgical results in the group of cyanotic, under 5Kg of body weight should be improved by means of more precise preoperative diagnoses, more advanced surgical techniques and more proper postoperative management.