Background: Physiological and procedural factors lead to hyperlactataemia, which is common in and following cardiac surgeries. Higher levels of lactate are typically signs of hypoxia in the tissues or they are linked with cardiopulmonary bypass (CPB) and aortic cross–clamp time (ACC). Lactate levels during cardiac surgery ought to be observed because it could be a sign of sufficiency of tissue perfusion and oxygen delivery. The correlation between CPB time, aortic cross–clamp (ACC), and lactate levels, though of clinical significance, is inconsistent among patients of different groups. The aim of this study is to evaluate the relationship between cardiopulmonary bypass time, aortic cross clamp time and lactate levels in the cardiopulmonary bypass surgery. The objectives are to investigate the lactate levels pre, post and during CPB, determine the relationship between the duration of CPB and intraoperative and postoperative lactate levels, examine the effects on the degree of postoperative hyperlactataemia of the ACC time, assess the relationship between a long CPB or ACC period and high risk of postoperative hyperlactataemia. Methods: A total of 100 adult patients underwent elective cardiac surgery along with CPB were included from the department of cardiac surgery at Alkhidmat hospital, Sahiwal, Pakistan. Prior to the comparison of CPB and ACC with the levels of lactate, data were collected. The baseline levels of lactate were measured with the preoperative arterial blood gas (ABG) and the postoperative levels were measured to determine the changes with time. Serial monitoring was used to calculate the lactate response relative to intraoperative factors. Demographic data such as age, gender, and type of the procedure were also documented and examined to study their possible impact on lactate processes and to detect any noticeable tendencies of the subgroups. Demographic and clinical data were analysed using descriptive statistics and the relationships between CPB time, ACC time and lactate concentration were assessed by correlation analysis as well as univariable and multivariable linear regression analysis. Stratified analysis by disease category and by gender was also performed to evaluate the differences in subgroups. A literature review related to the research was also conducted using a systematic manner. The review aimed to assess the general correlation between longer CPB and ACC times and lactate levels as well as postoperative outcomes. The review found that the studies are inconsistent and differences in methodology among the studies suggested that additional research was needed to assess the independent role of these on lactate production in adults undergoing cardiac surgery. Results: A large proportion of the study population comprised of males (65%) and females (35%) with a majority having undergone a coronary artery bypass grafting. Mean cardiopulmonary bypass time (CPB) was 139.4 minutes (SD 17.1), ACC time was 78.6 minutes (SD 15.4), and mean lactate level was 1.93 mmol/L (SD 0.54). The results of the correlation analysis indicated a positive strong correlation between CPB time and ACC (r = 0.819, p < 0.001) but there was no significant correlation between lactate levels and demographic factors (age, body surface area). Univariable regression analysis revealed that CPB time (0.021, p < 0.001) and ACC time (0.020, p < 0.001) had a significant effect on the prediction of lactate concentration, and 31.0% and 43.8% of the variance, respectively. But in the multivariate model, CPB time was still a significant independent predictor of lactate levels (0.020, p < 0.001), but ACC time was not significant (p= 0.744). Gender and disease stratified analyses showed that positive trends existed between CPB duration and lactate concentration, and through subgroups. Conclusion: These results indicate that although CPB and ACC are significant intraoperative parameters, CPB time is the only variable that predicts lactate concentration independently when the two are used simultaneously. The research has made an addition to the existing knowledge by demonstrating that lactate elevation in cardiac surgery is multifactorial, especially concerning the duration of perfusion and metabolic response. This offers a more sophisticated outlook on the intraoperative assessment and evaluation of lactate. The study needs to be carried out on a bigger scale in future involving more classes of diseases and different centres where the study will expand the generalisability and help explain the determinants and clinical outcome of hyperlactataemia further. Keywords: Cardiopulmonary Bypass time, Aortic Cross Clamp time, Hyperlactataemia, Cardiac surgery