A case of arrhythmogenic right ventricular dysplasia in a 10 year old girl is described which provides some evidence for an inherited aetiology of this unusual form of heart disease. The parents of this child were first cousins, thus increasing the possibility of inherited disorders in their offspring. She had been known from infancy to have the rare disorder of congenital deficiency of intestinal enteropeptidase, and low serum immunoglobulins G and A. An untyped adenovirus was grown from a myocardial biopsy taken early in the course of her cardiac disease. However, it is unlikely that this virus was a major factor in the aetiology of her cardiac disease. Both the cardiac and intestinal diseases are now commonly believed to result from hereditary factors, and this report provides further support for this view.