Two-dimensional echocardiography and Doppler echocardiography were performed in 19 patients with Duchenne muscular dystrophy for evaluating right ventricular overload and left ventricular function. Five of 19 patients were treated with mechanical ventilation. We defined right ventricular overload as right ventricular enlargement and the presence of paradoxical ventricular septal motion. The right ventricular dimensions in patients with mechanical ventilation were significantly larger than in patients without mechanical ventilation (p less than 0.01). All the patients with and without mechanical ventilation showed no significant right ventricular enlargement and none of them showed paradoxical ventricular septal motion. As for left ventricular function, there were no significant differences in the incidence of regional or diffuse wall motion abnormalities between two groups. However, the left ventricular fractional shortening was significantly lower in patients with mechanical ventilation than in patients without it (p less than 0.05), and the incidence of mitral regurgitation was significantly higher in the former than in the latter (p less than 0.01). Our findings suggest that right ventricular function is preserved even in patients with respiratory failure by appropriate respiratory treatment. Therefore, we should give attention to the progression of left ventricular dysfunction in long term prognosis.