A 23-year-old man with X-linked Becker type muscular dystrophy underwent cardiac transplantation because of dilated cardiomyopathy which was complicated by terminal heart failure. Impairment of muscle function was mild and slowly progressive, whereas the cardiac disease was severe and rapidly progressive. All four chambers of the removed heart were grossly dilated; microscopically, the myocardial fibres were hypertrophic and pale; the nuclei exhibited pleomorphism with variability in nuclear size, shape, and depth of staining.