The electrophysiological effects of stem cell based therapies for heart repair have not been systematically analyzed. To adress this issue, male Wistar rats with one-month old myocardial infarction were treated with intra-myocardial injection of (i) Insulin-like Growth Factor-1 (IGF-1) + Hepatocyte Growth Factor (HGF), (ii) cardiac progenitors cells (CPCs) or (iii) CPCs supplemented with HGF+IGF-1. Ventricular arrhythmias (VAs) were recorded prior and two weeks after treatment. Before sacrifice, invasive echocardiographic and/or hemodynamic measurements were perfomed. The heart was then perfusion-fixed for morphometric and immunohistochemical studies. All treatments determined a positive left ventricular remodelling and an amelioration of mechanical function associated with formation of new electro-mechanically competent myocytes and vascular structures. Whereas, VAs were reduced only when growth factors were injected, either alone or added to CPCs. The data are expected to be of interest to the broad readership of both basic and clinically oriented cardiovascular research, given the finding that lethal arrhythmias are responisble for up to half the death in heart failure.