Background: Diet-induced obesity is associated with several cardiovascular diseases and myocardial apoptosis. This study aimed to investigate the effect of high intensity interval training (HIIT) on the myocardial apoptosis in the diet-induced obese rats. Methods: Thirty-two male rats, after an obesity induction period, were randomly selected and assigned to four groups including non-obese control (NOC; n=8), basal obese control (BOC; n=8), obese control (OC; n=8), and obese+HIIT (OT; n=8). NOC and BOC groups were sacrificed before the training period. The OT group underwent a HIIT program performed 5 times/week over 12 weeks. Rat hearts were removed 48 hours after the last training session. The Bax, Bcl-2, cytochrome-c, Bid, caspase-8, as well as caspase-3 protein expressions were analyzed using western blotting. Data were analyzed using independent t test. Results: After obesity induction period, the Bax, Bid, cytochrome-c, caspase-8, caspase-3 proteins, and Bax/Bcl-2 in BOC were found to be significantly higher than those in NOC (P=0.025, P=0.0001, P=0.013, P=0.017, P=0.01, P=0.18, respectively). However, Bcl-2 protein in BOC was detected to be significantly lower than that in NOC (P=0.025). The results obtained after completing HIIT training showed that Bid, cytochrome-c, caspase-8, caspase-3, and Bax/Bcl-2 in OT were lower than those in OC (P=0.005, P=0.039, P=0.001, P=0.04, P=0.05, respectively). However, Bcl-2 protein in OT was significantly higher than that in OC (P=0.004). No significant difference was found between OT and OC regarding Bax protein (P=0.32). Conclusion: Diet-induced obesity may have exacerbated the myocardial apoptosis through both intrinsic and extrinsic pathways. However, it seemed that HIIT training significantly prevented the increase of myocardial apoptosis in obese rats.