PURPOSE: This study aimed to compare postoperative ejection fraction (EF) in response to coronary artery bypass grafting (CABG) among patients with preoperative EF <35% and >35%. METHODS: A retrospective study was conducted in a single institution using clinical data of 660 patients undergoing elective on-pump CABG in 2018-2019. Patients were classified into two groups based on preoperative left ventricle ejection fraction (<35% and >35%). The primary endpoint was the change of postoperative ejection fraction. RESULTS: In this study, 72 patients had preoperative left ventricle ejection fraction <35% (group A) while the other 588 patients had ejection fraction >35% (group B). Among both groups, the duration of cardiopulmonary bypass (CPB) and aortic clamp (AxC) were not significantly different (P > 0.05). The transformation of pre- and postoperative EF in groups A and B was significantly different (2.91+10.31 vs. -0.14+4.57, P < 0.001). There was a significant difference in the duration of ICU stay (73.42+112.55 vs. 34.43+64.99, P < 0.001) and postoperative ventilatory support (25.54+43.92 vs. 16.42+45.87, P < 0.008) between group A and B. CONCLUSION: Low preoperative EF showed better improvement in cardiac function after surgery. We concluded that the result could be affected by revascularization of hibernating myocardium.