We examined the influence of left ventricular diameter on surgical outcomes after isolated coronary artery bypass grafting (CABG) in patients with left ventricular ejection fraction (LVEF) <35%. The subjects were patients who underwent isolated CABG with and without cardiopulmonary bypass from January 2015 to the end of August 2023. Twenty-four patients were categorized into the LVEF ≥55% group( group N) and 14 patients into the LVEF ≤35% group( group L). Ten patients in group L were categorized into the group L-1 [moderately or more enlarged LV according to the left ventricular end-diastolic diameter (LVEDD) index (LVEDD/body surface area)]. Primary endpoints were allcause mortality, major complications, and postoperative hospitalization rate of more than 14 days. Complication rates were not statistically different between group N and L. The results were similar between group N and L-1. However, the group L had a significantly higher rate of hospitalization for 14 days or more after surgery compared with that in the group N (p=0.007). Similarly, the rate of hospitalization for more than 14 days was significantly higher in the group L-1 than that in the group N( p= 0.029). In patients with LVEF ≤35% undergoing isolated CABG, postoperative outcomes were similar to those with LVEF ≥55%, regardless of LV enlargement.