Background Although the safety and feasibility of combined coronary artery bypass grafting (CABG) and bone marrow stem cell (BMSC) transplantation have been proven, the efficacy of this approach remains controversial. Therefore, we conducted an updated meta-analysis of randomized controlled trials to evaluate the efficacy of this procedure. Methods Electronic databases were systematically searched for randomized trials comparing 4-month to 6-month follow-up outcomes in patients who underwent isolated CABG (CABG group) and patients who received BMSC transplantation with CABG (BMSC group). A random-effects meta-analysis was conducted across eligible studies. Meta-regression and subgroup analyses were utilized to identify sources of data heterogeneity. Results Thirteen trials were eligible, with a total number of 292 patients in the BMSC group and 247 patients in the CABG group. Compared with the CABG group, the BMSC group showed significant improvement of follow-up left ventricular ejection fraction (n = 539, 4.8%; 95% confidence interval [CI], 2.3%-7.3%; P = .001). The analyzed data showed significant heterogeneity (I2 = 74.2%, P < .001). The reduction in scar size (n = 120; -2.2 mL; 95% CI, -18.2 mL to 13.7 mL; P = .44) and the improvement in the 6-minute walk test (n = 212; 41 m; 95% CI, -13 m to 95 m; P = .10) did not reach statistical significance. No significant correlation was found between the number of the injected BMSCs or the method of injection and the change in ejection fraction. Conclusions The present evidence suggests that combined CABG and BMSC transplantation is associated with improvement of left ventricular ejection fraction. However, the heterogeneity in the data suggests variations in patient response to this therapy. Further studies are required to understand these variations.