Abstract: AIM To investigate the effect of aerobic interval training (AIT) on the cardiac mitochondrial function in aged mice hearts by SIRT3 mediated antioxidant enzyme system. METHODS Aged C57 mice (20 months) and adult C57 (4 months) mice were included in this study. AIT protocol consisted of 10-min warm-up period, 7-min interval training (4 min high-intensity and 3 min low-intensity training) and 1 min cool down. Training was performed for 1 h/day and 5 days/week for 12 weeks. Protein immune blot method (Western blot) was used to detect myocardial mitochondrial antioxidant enzyme related protein expressions. RESULTS AIT significantly increased the myocardial mitochondrial deacetylase sirtuin-3 (SIRT3) level and improved AMP-dependent protein kinase (AMPK) phosphorylation level in the aged hearts (P<0.05). Subsequently, AIT improved the activity of myocardial mitochondrial antioxidant enzymes (MnSOD, catalase) in the aged hearts. AIT also reduced the myocardial lipid peroxidation damage and improved the myocardial mitochondrial biosynthesis ability in the aged hearts (P<0.05). CONCLUSION AIT effectively increases the cardiomyocyte SIRT3 level in aged mice and improves myocardial mitochondrial functions. The cardioprotective mechanism of AIT may be related to the activation of myocardial SIRT3 mediated by the antioxidant enzyme system.