Background: Previous studies showed improvement in heart function by injecting bone marrow mesenchymal stem cells (BMSCs) after AMI. Emerging evidence suggested that both the number and function of BMSCs decline with ageing. We designed a randomized, controlled trial to further investigate the safety and efficacy of this treatment. Methods: Patients with ST-elevation AMI undergoing successful reperfusion treatment within 12 hours were randomly assigned to receive an intracoronary infusion of BMSCs (n = 21) or standard medical treatment (n = 22) (the numbers of patients were limited because of the complication of coronary artery obstruction). Results: There is a closely positive correlation of the number and function of BMSCs vs. the cardiac function reflected by LVEF at baseline (r = 0.679, P = 0.001) and at 12-month follow-up (r = 0.477, P = 0.039). Six months after cell administration, myocardial viability within the infarct area by 18-FDG SPECT was improved in both groups compared with baseline, but no significant difference in the BMSCs compared with control groups (4.0 +/- 0.4% 95%CI 3.1-4.9 vs. 3.2 +/- 0.5% 95%CI 2.1-4.3, P = 0.237). 99mTc-sestamibi SPECT demonstrated that myocardial perfusion within the infarct area in the BMSCs did not differ from the control group (4.4 +/- 0.5% 95%CI 3.2-5.5 vs. 3.9 +/- 0.6% 95%CI 2.6-5.2, P = 0.594). Similarly, LVEF after 12 and 24 months follow-up did not show any difference between the two groups. In the BMSCs group, one patient suffered a serious complication of coronary artery occlusion during the BMSCs injection procedure. Conclusions: The clinical benefits of intracoronary injection of autologous BMSCs in acute STEMI patients need further investigation and reevaluation. (C) 2013 Elsevier Ireland Ltd. All rights reserved.