Abstract: AIM To explore the protective action of melatonin (Mel) against myocardial ischemia/reperfusion (MI/R) injury and its association with myocardial Notch1/Hes1 signaling pathway. METHODSNinety male Sprague Dawley rats weighing 200-250 g were subjected to myocardial ischemia/reperfusion (MI/R, I 30 min, R 4 h) by occluding the left descending artery and were randomly divided into three groups: MI/R+V (absolute alcohol diluted in sterile saline to 0.1 M, 1 ml/day, 4 weeks), MI/R+Mel ［10 mg/(kg·day), 4 weeks before MI/R］ and sham (rats undergoing the same surgical procedures without tying the suture). After 4 h of reperfusion, myocardial NICD (Notch1 intracellular domain), Hes1, PTEN, p-Akt/Akt ratio and apoptotic related protein expressions were measured. After 6 h of reperfusion, myocardial apoptotic index and infarct size were evaluated. Cardiac functions were measured 72 h after reperfusion. RESULTSMel treatment significantly improved cardiac functional recovery and reduced myocardial apoptosis (P<0.01). Additionally, Mel treatment modulated PTEN/Akt signaling by activating Notch1/Hes1 signaling (P<0.05). CONCLUSIONOur results show that melatonin protects the heart against MI/R injury by reducing apoptosis, possibly through Notch1/Hes1 signaling pathway.