Duchenne muscular dystrophy is the commonest genetic muscular disease. The prognosis, which depends on cardiac involvement, is poor. In boys, this takes the form of a hypokinetic cardiomyopathy particularly affecting the postero-lateral wall of the left ventricle which then dilates. The recent identification of the gene which transmits the disease on the X chromosome and of the coded protein, dystrophin, has improved our understanding of the disease. We report two cases of isolated cardiac involvement in two female carriers of the disease, classically thought to be unaffected. They presented with apparently idiopathic dilated cardiomyopathies. These cases show that Duchenne muscular dystrophy is an original example of a genetically determined diffuse muscular disease with cardiac involvement.