OBJECTIVES: Cell therapy may offer novel therapeutic options for chronic ischemic heart disease. In a clinical trial, we first assessed the feasibility and safety of intramyocardial CD133+ bone marrow cell injection together with coronary artery bypass grafting (CABG). We then tested the hypothesis that CABG plus CD133+ cell injection would result in better contractile function than CABG alone. METHODS: Fifteen patients took part in the safety study, followed by 40 patients who underwent either CABG with cell therapy or CABG alone. Bone marrow was harvested from the iliac crest one day before surgery, and purified CD133+ progenitor cells were injected in the infarct border zone during the CABG operation. LV function was measured by echocardiography and myocardial perfusion by SPECT. RESULTS: In the safety study, no procedure-related complications were observed for up to 3 years. LV injection fraction (LVEF) increased from 39.0% +/- 8.7% preoperatively to 50.2% +/- 8.5% at 6 months and 47.9% +/- 6.0% at 18 months (F = 6.03, P = .012). In the efficacy study, LCEF rose form 37.4% +/- 8.4% to 47.1% +/- 8.3% at 6 months in the group with CABG and cell therapy (F = 24.16, P < .0001) but only from 37.9% +/- 10.3% to 41.3% +/- 9.1% in the CABG-only group (F = 7.72, P = .012). LVEF was significantly higher at 6 months in the group with CABG and cell therapy than in the CABG-only group (P = .03). Similarly, perfusion of the infarcted myocardium improved more in patients treated with CABG and cell therapy than in those treated with CABG alone. CONCLUSION: Intramyocardial delivery of purified bone marrow stem cells together with CABG surgery is safe and provides beneficial effects, though it remains to be seen whether thewe effects produce a lasting clinical advantage.