Between January 1980 and July 1984, 321 cases of open heart surgery for infants or small children under 10Kg of body weight were performed, which occupied the great part of total open heart surgery done in the same period. The mean age was 16.58.7 months [ranging from 2 days to 51 months], and the mean body weight was 7.8a1.8Kg [from 2.8 to 10Kg] which was below the third percentile compared with the mean age. The technique of deep hypothermia with total circulatory arrest, which contributed to great improvement in operative condition, was used increasingly and widespreadly in this period. For each anomaly, the number of patients and operative deaths were as follows: VSD, 11 of 184 [6.0%]; TOF, 8 of 47 [17.8%]; TGA, 13 of 30 [43.3%]; ASD, none of 9; TAPVR, 1 of 8 [12.7%]; C-ECD, 3 of 6 [50%]; Tricuspid Atresia, 4 of 5 [80%]; Pulmonary Atresia, 2 of 4 [50%]; Congenital Mitral Anomaly, 1 of 3 [33.3%]; P-ECD, none of 3