Background : Duchenne and Becker muscular dystrophies are caused by mutation in dystrophin gene essential for muscle function. Recent advances in non-invasive ventilation reduced the mortality from respiratory insufficiency and cardiac involvement has been considered as a main clinical problem in patients with progressive muscular dystrophy (PMD). Patients with PMD exhibit left ventricular (LV) systolic dysfunction similar to that in patients with idiopathic dilated cardiomyopathy (DCM). However, it has been known that the patients with PMD have lower plasma brain natriuretic peptide (BNP) and less congestive heart failure symptoms compared to patients with DCM, even with similar LV ejection fraction (EF). We therefore hypothesized that the patients with PMD may have more favorable prognosis. Methods : Forty-nine patients with PMD were studied (Duchenne 44, Becker 5). The diagnosis was made on the basis of physical findings, family history, electromyography and muscle biopsy. The mean age of the patients with muscular dystrophy was 21 years (range: 15-35). At the time of enrollment, the patients underwent transthoracic echocardiography and measurement of plasma BNP. Then the patients were monitored for the occurrence of clinical events (death, worsening of heart failure, and hospitalization due to cardiac causes). Results : Median LVEF was 42% (range 7-76%), and median BNP was 11.8pg/mL During follow-up (mean: 10짹5.8 month), there were 3 clinical events (2 deaths from cardiac cause and 1 death from noncardiac cause). In multivariate analysis, both LVEF and plasma BNP could not predict clinical events. Conclusions : The incidence of clinical events was lower than expected in patients with PMD despite low LVEF. The prognosis of the patients with PMD may be relatively benign. Cardiac dysfunction in the patients with PMD could not predict clinical event in this study.