Objectives: Although the mortality rate of primary ventricular septal defect (VSD) closure surgery has been reduced to <0.5% in many centers, low cardiac output syndrome and multi-organ failure syndrome development in the post-operative period are still the most common causes of mortality and morbidity. The use of biochemical markers in the early period can be used as effective predictors for reducing mortality and morbidity. In this study, the effect of post-operative serum lactate and cardiac troponin I (cTNI) levels on hospital mortality in patients who underwent primary closure of VSD was investigated retrospectively. Methods: The effect of lactate and cTNI values on hospital mortality in 52 patients who underwent surgical repair for VSD was investigated. Serum lactate levels of all patients in the first 6 h after the operation; on the first post-operative day, cTNI values were examined retrospectively. Serum lactate levels exceeding 3.5 mmol/ lt and cTNI values exceeding 35 ng/mL were determined as the cut-off points. Results: Serum lactate level and cTNI increase were found to be statistically different in the mortality group (p<0.05). It was shown that increased cTNI was associated with weight, left ventricular end-diastolic diameter, and cardiopulmonary bypass time (p<0.05). Serum lactate levels were 4.1±0.5 mmol/lt in the non-mortality group and 15.3±8.3 mmol/lt in the mortality group, and the difference was statistically significant (p<0.05). Hospital mortality was observed in 6 patients. Conclusion: In patients undergoing VSD closure surgery, serum lactate levels measured in the first 6 h postoperatively and cTNI levels measured on the first post-operative day are associated with hospital mortality. Concomitant elevations of lactate and cTNI values in patients after VSD closure should suggest to take caution and early supportive treatments to reduce mortality.