OBJECTIVE This study was aimed to investigate the changes of plasma glucose during/after cardiopulmonary bypass.METHODS 123 congenital heart defect cases,male,40;female,83,were divided to four groups. Group 1,non-cardiopulmonary bypass cases;Group 2, cases with the cardiopulmonary bypass time less than 60 minutes; Group 3, cases with the cardiopulmonary bypass time between 60 to 120 minutes; Group 4, cases with the cardiopulmonary bypass time more than 120 minutes. All the arterial blood samples were taken at different time points. RESULTS The plasma glucose levels in the longer cardiopulmonary bypass cases were proved to be higher than the shorter ones. Our study also showed that the levels in plasma glucose of longer cardiopulmonary bypass time groups revered slowlier.CONCLUSION Hyperglycemia after cardiopulmonary bypass must be dealt with carefully and actively.