Objective: To determine the effect of MUF on pre and post MUF lactate levels. Study Design: Analytical Cross-sectional study. Place and Duration of Study: Pediatric Operation Theater at Armed Forces Institute of Cardiology/National Institute of Heart Disease, Rawalpindi Pakistan from Oct 2021 to Dec 2021. Methodology: It was descriptive cross-sectional study and non-probability consecutive sampling technique was used. Data was collected during Oct 2021 to Dec 2021, from Tertiary Care Hospital, Rawalpindi Pakistan. Current study was conducted in pediatric OT at Armed Forces Institute of Cardiology/National Institute of Heart Disease. MUF technique was applied to 115 pediatric patients during congenital cardiac surgeries. Pre and post MUF lactate levels were noted. Inferential statistics were applied with the help of test of significance (Paired T-Test), p value ≤ 0.05 was considered statistically significant at 95% Confidence Interval (CI) with margin of error 5%. Collected data was analyzed by IBM SPSS version 25. Result: Significant decrease in post MUF lactate level (p<0.05) was observed. This result revealed that MUF had significant effect on lactate levels. Out of 115 study participants, 46(40%) were female and 69(60%) were male patients having mean age 3.44±2.25 years, mean height 95.60±18.78cm, mean weight 15.06±5.18kg, mean body surface area 0.63±0.17 m2 CPB time 127.95±36.78 minutes and cross clamp time 92.60±40.49 minutes. Paired t-test was applied to check the mean difference between pre and post lactate levels and it revealed statistically significant findings (p-value < 0.05). Conclusion: Current result revealed that use of MUF caused decrease in lactate levels. MUF technique showed beneficial effects in maintaining normal physiology of the body. Current results encouraged the use of MUF technique in every cardiac surgery.