Objective: Stem cell therapy has gained great attraction in the treatment of acute and chronic myocardial diseases in recent years. The aim was to evaluate our experience in light of the middle term results of intramyocardial stem cell treatment with concomitant coronary artery bypass surgery (CABG) since 2001. Methods: After encouraging initial results of the Phase I (safety) trial with the first 15 patients, a prospective, controlled Phase II (efficacy) study was begun with 40 patients aiming to determine functional benefit of stem cell treatment using bone marrow derived CD 133+ stem cell therapy with concomitant CABG in comparison to CABG only since 2003. Medium-term results of intervention were evaluated using patient’s clinical findings, Holter monitoring, echocardiography, magnetic resonance imaging, computed tomography and myocardial scintigraphy. Statistical analyses were performed using unpaired t, Mann-Whitney U, ANOVA for repeated measurements and Chi-square tests. Results: Left ventricular ejection fraction (LVEF) has increased significantly at 6th and 18th months follow-up in the first 15 patients who received therapy since 2001 (preoperative: 39.0±8.7%; 6th month: 50.2±8.5% and 18th month: 47.9±6.0%; p=0.012). In the late group of patients, LVEF increased from 37.4±8.4% to 47.1±8.3% (p<0.001) whilst although an increase in LVEF has been observed in the CABG alone group (from 37.9±10.3% to 41.3±9.1%) the increase has not been statistically significant. Mortality occurred in 2 patients [1 patient from the early and 1 patient from the medium term follow-up] due to non-cardiac reasons. Myocardial calcification, lethal ventricular arrhythmia, and tumor formation have not been observed in any of the patients in the long-term follow up. Conclusion: Direct injection of bone marrow derived CD 133+ stem cells into the myocardium with concomitant CABG is safe. However, this treatment modality may only be applied as standard treatment after completion of the long term detailed results of prospective, randomized multicenter trials.