Background: Changes in the electrocardiogram (ECG) and an increase in the release of biochemical markers are used to diagnose perioperative myocardial infarction. Candidates with high levels of troponin T and creatine kinase (CK)-MB have been found to be particularly promising. Unfortunately, CK activity and (CK-MB) are not entirely reliable in terms of their sensitivity and specificity. Aim & objectives: to assess the effect of reperfusion injury on the cardiac function as assessed by LDH, CK, CK-MB, troponin I, in addition to ECG and ECHO. Patients and Methods: The research was prospective, meaning that it looked into the future. conducted on Cardiothoracic Department, Mansoura University Hospitals. The study comprised 23 patients subjected to open heart surgery and were separated into two groups: Group I (Ventricular septal defect group) and Group II (Valve replacement group). Results: there was a statistically significant difference amongst the 2 groups regarding to One way Anova for mean LDH levels, total CK levels, CK-MB levels, Troponin I levels and postoperative ischaemic changes via ECG. There was no statistically significant difference among the 2 groups regarding to Comparison of LDH levels at different times and Correlation between LDH, total CK, CK-MB and Troponin I levels at different times with both ischaemic and perfusion times. Conclusion: The use of laboratory panels for assessment of an organ function is advocated by many clinicians. Laboratory markers of cardiac damage are now widely used, especially when false negative ECG changes are taken into consideration.