Abstract Background: Hypothermia is known for its adverse effects on coagulation cycle that could be of clinical significance for patients undergoing elective coronary artery bypass surgery. Aim of Study: The aim of this prospective study was to evaluate the influence of core temperature on postoperative amount of blood loss, transfusion requirements, coagulation profile and the length of hospital stay in patients undergoing elective on pump coronary artery bypass grafting operations Patients and Methods: As regarding the methodological approach for the intended research, well formulated objectives are made with study design of prospective observational comparative study at Ain Shams University cardiothoracic hospital, from May 2022 till August 2022. Regarding the sample size: By using PASS 11 program for sample size calculation, setting power at 99%, alpha error at 5% and after reviewing previous study results showed that the amount of blood loss was significantly larger in hypothermic group (185.667±41.34) compared with normothermic group (516.033 ±41.536). Based on that: A sample size for 60 patients under-going coronary artery bypass surgery (divided into 2 groups-30 patients in each group) will be sufficient to achieve study objective. The patients will be divided into 2 groups. In normothermic group (n=30) patients will be warmed by warming fluids and mattresses warmers, however patients whom belong to the hypothermic group (n=30), will be allowed to develop hypothermia. Exclusion criteria includes patients with pre-existing hypothermia (<36 C) or hyperthermia (>38 C), a postoperative temperature >38 C. Results: The amount of blood loss (bleeding) was much larger in hypothermic group than normothermic group (p<). The amount of blood units transfused was significantly higher in hypothermic group than normothermic group. The PTT and PT were more prolonged in hypothermic group compared with normothermic group. There was a noticed correlation as in increased length of hospital stay in hypothermic group compared with normothermic group. Conclusion: The study demonstrates that hypothermia is associated with increased amount of postoperative bleeding/blood loss and the number of blood units transfused in patients underwent elective on pump coronary artery bypass grafting surgery.