Ventricular arrhythmias and sudden death are a common complication of heart failure. Cellular cardiomyoplasty is thought to enhance left ventricular function, but it remains unclear if this therapy also improves cardiac electrical stability after myocardial infarction. Adult male mice underwent cryo-infarction and transplantation of electrically coupling embryonic cardiomyocytes (ECM) and non-coupling skeletal myoblasts (SMB). In vivo transvenous electrophysiological testing, including evaluation of the inducibility of ventricular tachycardia (VT) was performed in these and control (WT) mice. All non-treated, infarcted mice were susceptible to induction of VT. Transplantation of ECM strongly reduced VT-inducibility (37.5 %; p=0.0009) to control-level (WT: 40%). In contrast, the VTs deteriorated in the SMB-group (still 100% inducible; p=0.0011 vs. WT; p=0.0009 vs. ECM) as 4 mice developed persistent VTs and ventricular fibrillation; the VTs in all other groups were self-terminating. Hence, transplantation of electrically non-coupling SMB causes a deterioration of the electrical stability. Importantly, transplantation of ECM electrically stabilized the acutely injured mouse heart and may represent a novel therapeutic strategy for the treatment of malignant arrhythmias.