Myocardial involvement is a common finding in patients with Duchenne-type muscular dystrophy (DMD). Nevertheless, the prognostic values of standard electrocardiogram (ECG), ventricular arrhythmias, ventricular late potentials (LPs), and left ventricular (LV) systolic dysfunction have not been extensively investigated. Eighty-four patients with DMD (aged 18.6 ± 4.8 years) underwent standard and signal-averaged electrocardiography, 24-hour Holter monitoring, and echocardiography. The prevalence of electrocardiographic abnormalities, frequent ventricular premature complexes, LPs, and LV systolic dysfunction was 71%, 32%, 28%, and 35%, respectively. Median follow-up was 76 months (range 5 to106). The mortality rate in the follow-up period was 27%. The typical DMD electrocardiographic alterations, ventricular arrhythmic pattern, and LPs were not predictors of mortality. In contrast, the presence of LV systolic dysfunction detected on echocardiography was a powerful predictor of mortality in the follow-up period (p = 0.013, hazard ratio 3.14, 95% confidence interval 1.27 to 7.79). Thus, echocardiographic assessment of LV systolic dysfunction provides prognostic information in patients with DMD. Electrocardiographic alterations, ventricular arrhythmias, and LPs have no prognostic value in predicting mortality in these patients.