Background: Fluctuations in glucose levels and prolonged hyperglycaemia is associated with poor outcomes concerning morbidity and mortality in cardiac surgery patients. Paediatric patients are more susceptible to adverse effects of hyperoxaemia during cardiopulmonary bypass (CPB) on glucose homeostasis. In this study, we tried to find out changes in blood glucose and the Insulin requirements intraoperatively in paediatric patients undergoing cardiac surgery requiring CPB. This is a prospective, single-centre study performed among 130 paediatric patients of either sex in the age group below 12 years with congenital heart disease scheduled for cardiac surgery requiring CPB. The parametric data were analyzed by paired t-test for intragroup comparison and unpaired t-test for intergroup comparisons. Differences were significant when the probability was less than 0.05 (p-value). Chi-square test was used for inferential data analysis. Blood glucose was meticulously monitored at various points of time as at baseline, after 10 min, then every half-hourly during bypass, 30 minutes after bypass, and after 10 min at intensive care unit (ICU). To control blood glucose on CPB inj. Insulin was used as per study protocol. Group I (n= 97) patients required insulin due to hyperglycaemia on CPB while Group II (n=33) no insulin was required on CPB. 74% of paediatric patients required insulin on cardiopulmonary bypass out of the 43% required insulin 30 min after starting CPB. There is significant blood glucose rise in children of congenital cardiac disease after induction of anaesthesia, and on CPB. The duration of CPB might not significantly affect the insulin requirement of patients. CPB significantly affected glucose homeostasis in children. Hence it seems prudent to administer a small amount of intravenous dextrose in the pre-bypass period to avoid hypoglycaemia. The insulin administration rate and dose should be adjusted on CPB as per patient requirements