The long-term safety and efficacy of autologous bone marrow cell implantation into the myocardium remains undefined. We studied the long-term clinical outcome of 12 patients with severe coronary artery disease who underwent electromechanical mapping-guided catheter-based autologous bone marrow cell implantation. Magnetic resonance imaging at 3 and 6 months showed no evidence of intramyocardial tumor formation, myocardial damage, or worsening of left ventricular ejection fraction. No sustained arrhythmia was detected on 24-hour Holter monitoring. After 44 +/- 10 months of follow-up, 1 patient had died of stroke at 8 months and another patient had died of myocardial infarction at 20 months. Computed tomography at 36 months or postmortem examination showed no tumor formation or intramyocardial calcification at the treated sites, and no sustained ventricular arrhythmia or sudden death was observed. Autologous bone marrow cell implantation into the ischemic human myocardium was not associated with long-term major adverse events regarding tumor, scar, or calcification formation, and the arrhythmogenic risk was low.