We report a study, assessing involvement of the heart in 33 familial cases of Becker muscular dystrophy (BMD), 31 familiar cases of facioscapulohumeral (FSH) dystrophy, and 27 familial cases of Bethlem myopathy. In the patients with BMD, correlations of myocardial involvement with age and extent of musculoskeletal involvement were made. We performed physical examination, chest x-ray, electrocardiographic (EKG), and echocardiographic examination on all patients, and continuous EKG Holter-monitoring in the patients with FSH dystrophy. Thirteen patients with BMD (45%) showed EKG changes similar to those found in Duchenne muscular dystrophy. Only 1 of the 13 individuals with cardiac involvement was wheelchair-bound. We found no evidence of cardiac changes in the patients with FSH dystrophy. In Bethlem myopathy, only 1 patient had a form of hypertrophic cardiomyopathy (asymmetrical septal hypertrophy).