The scar border zone is a main source of reentry responsible for ischemic ventricular tachycardia (VT). We evaluated the effects of mesenchymal stem cell (MSC) injection into the scar border zone on arrhythmic risks in a post-myocardial infarction (MI) animal model. Rabbit MI models were generated by left descending coronary artery ligation. Surviving rabbits after 4 weeks underwent left thoracotomy and autologous MSCs or phosphate-buffered saline (PBS) was administered to scar border zones in two rabbits in each group. Another rabbit without MI underwent a sham procedure (control). An implantable loop recorder (ILR) was implanted in the left chest wall in all animals. Four weeks after cell injections, ventricular fibrillation was induced in 1/2 rabbit in the PBS group by electrophysiologic study, and no ventricular arrhythmia was induced in the MSC group or control. Spontaneous VT was not detected during ILR analysis in any animal for 4 weeks. Histologic examination showed restoration of connexin 43 (Cx43) expression in the MSC group, which was higher than in the PBS group and comparable to the control. In conclusion, MSC injections into the MI scar border zone did not increase the risk of VT and were associated with favorable Cx43 expression and arrangement.