OBJECTIVE: To investigate the protective effect of dynamin-related protein 1 (Drp1) in rats with myocardial ischemia/reperfusion injury (IRI). METHODS: ), reactive oxygen species (ROS) and ATP production were measured in rats. The myocardial tissues were harvested for the determination of the area at risk (AAR) and the infarct area (AI), and the ratio of AI/AAR was calculated. The expression of Drp1 and cytochrome C (Cyt C) was determined by Western Blot. RESULTS: : 6.40±1.40 vs. 8.90±1.50, ROS: 41 916.3±6 295.3 vs. 65 182.6±3 777.8], AI/AAR was significantly decreased (0.38±0.01 vs. 0.62±0.01), MMP and ATP were significantly increased [MMP: 0.78±0.13 vs. 0.38±0.07, ATP (μmol/g): 150.8±12.3 vs. 103.7±8.4], the expression of Drp1 was significantly decreased (0.50±0.02 vs. 0.79±0.05), expression of mitochondria Cyt C was significantly increased (0.64±0.04 vs. 0.21±0.01), and expression of cytoplasmic Cyt C was significantly decreased (0.48±0.03 vs. 0.78±0.04), and the differences were statistically significant (all P < 0.05). CONCLUSIONS: Mitochondrial fission was excessively high during IRI, and its function was significantly decreased. Drp1 inhibitor could inhibit the division of mitochondria, and improve its function and cardiac function.