This study was done to see the changes in the serum transaminase and LDH levels after general anesthesia in open heart surgery. We selected at random 60 patients who had received open heart surgery under cardiopulmonary bypass with mild to moderated hypothermia. They were divided into 3 groups depending on the anesthetic agents, halothane, penthrane and morphine group. Serum transaminase and LDH levels were checked before operation and also about 24 hours after operation; SGOP; spectrophotometirc assay by end-point method with Sequential Multiple Autoanalyser(SMA), SGPT; Spectrophotometric assay by kinetic method with SMA, LDH; Spectrophotometric assay by kinetic method. The results were as follows: 1) Serum transaminase and LDH levels were not significantly influenced by anesthetic agents after open heart surgery. 2) Serum transaminase and LDH levels were not significantly influenced by anesthetic agents in congental heart disease. 3) Serum transaminase and LDH levels were not significantly influenced by anesthetic agents in acquired heart disease.