Background: Patients with low ejection fraction who are undergoing coronary artery bypass graft (CABG) only have an insignificant improvement in ejection fraction. This condition will make a little hope to achieve an improvement in physical performance. But now, from a view study, CD133+ stem cells offer new hope for this situation. This study evaluates CD133+ bone marrow stem cells’ role for functional exercise capacity improvement in low ejection fraction coronary artery bypass graft patients. Methods: Thirty patients with ischemic heart disease who had ejection fraction<35% at the National Cardiovascular Center were randomized into 2 groups. The treatment group undergoes the CABG + CD133+ procedure and the control group undergoes the CABG only. All research subjects underwent follow-up before and 6 months after the procedure. Fraction ejection, scar size, wall motion score index, ventricular dimensions, myocardial perfusion measured by cardiac MRI, 6 Minutes Walking Test (6MWT) and Minnesota Living with Heart Failure Questionnaire (MLHFQ) as an additional parameter for physical performance and quality of life. Data was analyzed using SPSS version 21 for Windows. Results: The results of the fraction ejection parameters showed a significant improvement in the treatment group, from 25.88±5.66% to 34.57%±11.31% compared to CABG only 30.18±3.85% to 31.61±7.89% (p=0.040), in the perfusion defect showed improvement but not significant, left ventricular end-systolic volume and left ventricular end-diastolic volume showed improvement with no significant result, scar size was found to be an improvement in the treatment group 10 persons (76.92%) compared to the control group 5 persons (38, 46%) (p=0.040), the wall motion score index and 6MWT showed a significant improvement in the treatment group (p=0.003 and p=0.03, respectively). The MLHFQ parameter showed improvement but not significant. Conclusion: CD 133+ stem cell implantation in patients with low ejection fraction who undergo CABG provides improved myocardial function and indirectly improves functional exercise capacity and patients’ quality of life. © 2021, Sanglah General Hospital. All rights reserved.