--- - |2- Exercise training improves diabetic cardiomyopathy and heart function by decreasing the cardiac myocyte ER stress and subsequent myocardial apoptosis.This is an important finding because ER stress is one of the underlying mechanisms of diabetic complications. Thus, exercise training may significantly contribute to complication prevention in diabetes, which shows an intensity effect. Our findings reveal a novel mechanism of the effect of exercise in the management of diabetic cardiomyopathy. To explore the protective effect of exercise training on the injury of myocardium tissues induced by streptozotocin (STZ) in diabetic rats and the relationship with endoplasmic reticulum stress (ERS), the male sprague‐dawley (SD) rats were fed with high‐fat and high‐sugar diet for 4 weeks, followed by intraperitoneal injection of STZ, 40 mg/kg, to establish a diabetes model, and then 10 rats were randomly selected as diabetes mellitus (DM) controls and 20 eligible diabetic rats were randomized into two groups: low‐intensity exercise training (n = 10) and high‐intensity exercise training (n = 10). After 12 weeks of exercise training, rats were killed and serum samples were used to determine cardiac troponin‐I (cTn‐I). Myocardial tissues were sampled for morphological analysis to detect myocardial cell apoptosis, and to analyze protein expression of glucose‐regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), and caspase‐12. Different intensities (low and high) significantly reduced serum cTn‐I levels compared with the DCM group (p < 0.01), and significantly reduced the percentage of apoptotic myocardial cells and improved the parameters of cardiac function. Hematoxylin and eosin and Masson staining indicated that exercise training could attenuate myocardial apoptosis. Additionally, exercise training significantly reduced GRP78, CHOP, and cleaved caspase‐12 protein expression in an intensity‐dependent manner. These findings suggest that exercise appeared to ameliorate diabetic cardiomyopathy by inhibiting endoplasmic reticulum stress‐induced apoptosis in diabetic rats. - 'Journal of Cellular Physiology, Volume 234, Issue 2, Page 1682-1688, February 2019. '