BackgroundTransplantation of cardiosphere-derived cells (CDCs) has been shown to exert a therapeutic effect in patients with myocardial infarction (MI). However, poor survival of transplanted CDCs limits their beneficial effect. Metformin (MET) activates AMP-activated protein kinase (AMPK) which is associated with cell survival. The aim of this study is to determine whether MET improves CDC survival in the transplantation microenvironment and enhances the therapeutic effect of CDC transplantation against MI.