OBJECTIVE: The optimal surgical strategy for coronary artery bypass grafting (CABG) in patients with heart failure with reduced ejection fraction (HFrEF) is uncertain. This study aimed to compare postoperative outcomes between off-pump/on-pump CABG (OPCAB vs ONCAB) in patients with HFrEF. METHODS: This retrospective cohort study included adults with HFrEF undergoing CABG from the National Health Insurance Research Database, 2001-2021. Primary outcome was all-cause mortality. Secondary outcomes were postoperative complications. Logistic regression was used to determine associations by estimating odds ratios (ORs) with 95% confidence intervals (CIs). RESULTS: Data of 855 patients were analyzed (OPCAB n = 252; ONCAB n = 603). After multivariable adjustment, OPCAB was not significantly associated with all-cause mortality within 30 days compared with ONCAB. OPCAB was also not significantly associated with 31-day to one-year all-cause mortality, overall cardiovascular events, IS/TIA, AKI, infection other than pneumonia, sepsis, or pneumonia compared with ONCAB. In stratified analyses, OPCAB was associated with higher odds of sepsis among patients with less extent of coronary artery disease (<3-vessel disease) (aOR = 3.16, 95% CI: 1.24-8.07) and among those with cerebrovascular disease (aOR = 3.40, 95% CI: 1.13-10.21). CONCLUSIONS: In patients with HFrEF undergoing CABG, surgical approach (OPCAB vs ONCAB) was not independently associated with 30-day mortality, 1-year mortality, or major postoperative complications after adjustment. Further prospective studies with detailed operative and patient-level data are still warranted. What is already known on this topic: Both CABG and OPCAB are established revascularization strategies, but prior studies comparing their outcomes in patients with HFrEF have reported inconsistent results and were often limited by small sample sizes or single-centre designs.What this study adds: Using a nationwide Taiwanese cohort, this study shows that OPCAB is not independently associated with higher short-term mortality or major postoperative complications after adjustment for confounders in patients with HFrEF.