Abstract: AIM To evaluate the effects of diet and exercise intervention on left ventricular systolic function in obese rats. METHODS SD rats were fed with a high fat diet for 12 weeks and obese rats were then randomly divided into 4 groups: normal foodsedentary (HFD/NF-S), normal foodexercise (HFD/NF-Ex), high-fat diet-sedentary (HFD-S) and high-fat diet-exercise (HFD-Ex). After exercise training for 8 weeks, general data of the rats was recorded, blood lipid and blood sugar were detected. Left ventricular structure and function were measured by echocardiography and two-dimensional speckle tracking imaging for analysis of left ventricular strain and strain rate. By routine and special staining, myocardial collagen fibrils, mast cell infiltration, and autophagy were observed in the myocardium. Electron microscope was used to observe ultrastructure changes of the myocardium. RESULTS Compared with in the HFD/NF-Ex group, the rats blood glucose and blood lipid, degree of myocardial fibrosis, mast cell infiltration and autophagy in the HFD-S group increased significantly (P<0.01), and ventricular septal and left ventricular wall hypertrophy (P<0.05), strain and strain rate of left ventricular segments decreased (P<0.05).Compared with the other three groups, the results in the HFD/NF-Ex group were significantly improved. Results in the HFD/NF-S and HFD-Ex group were better than those in the HFD-S group but they were not superior to those in the HFD/NF-Ex group. CONCLUSION The intervention of diet combined with exercise postponed obese rat myocardial remodeling, myocardial fibrosis, and autophagy, which improved cardiac function. Single exercise or diet intervention reduced myocardial remodeling, fibrosis and autophagy in obese rats and improved cardiac function as well, but the effects were not as effective as the combined interventions.