Objective To study the effects of magnetic resonance imaging (MRI) on ventricular function in patients with idiopathic dilated cardiomyopathy (IDCM). Methods The data of 85 IDCM patients were retrospectively analyzed. According to the standard of cardiac function, they were divided into grade Ⅰ~Ⅱ (n=20), grade Ⅲ (n=35) and grade Ⅳ (n=30). The values of MRI and two-dimensional echocardiography (2DE) in evaluation of ventricular function were analyzed. Results There were different degrees of left and right ventricle dilation among 85 IDCM patients, mainly in left ventricular dilation. In MRI examination, there were 36 cases of left ventricular enlargement with the mainly spherical left ventricle and the thinner wall thickness, and there were 49 cases of bilateral ventricular enlargement with the diffusely weakened myocardial motion. 2DE examination showed that all patients were with complete heart enlargement, of which 56 cases were mainly left ventricular enlargement with thinner ventricular septum and left ventricular posterior wall thickness and diffusely weakened ventricular wall motion. With the increase of cardiac function grades in IDCM patients, the levels of LVEDV and LVESV by MRI were increased gradually while the levels of LVSV, LVEF, LVPER and LVPFP were gradually decreased, and there was significant difference among different grades (P<0.05). The LVESV level by 2DE was increased gradually while the LVEF level was decreased gradually, and the differences among the different grades of patients were significant (P<0.05). There was no significant difference in the thickness of ventricular septum, anterior wall and posterior wall between 2DE and MRI (P>0.05), but there were significant differences in the thickness of lateral wall and apex of heart(P<0.05). Conclusion Both 2DE and MRI can effectively assess the ventricular function of IDCM patients, but 2DE tends to underestimate left ventricular volume with poor reproducibility whereas MRI provides more parameters of left ventricular function and volume with high reproducibility. And MRI can more accurately assess the cardiac function and ventricular wall thickness, and it has high clinical application values.