A 49-year-old women with congestive heart failure and heart block died of cerebral embolism. Clinical and echocardiographic findings suggested a diagnosis of atypical dilated cardiomyopathy with predominantly right ventricular involvement. At necropsy, all the cardiac chambers were slightly dilated and the interventricular septum and the left ventricular wall were of normal thickness and symmetry. Histological examination, however, disclosed extensive disarray of abnormal myocardial tissue, especially in the interventricular septum. Her father had similar clinical and echocardiographic findings, while one of her brothers had typical hypertrophic cardiomyopathy at necropsy. It is likely that the patient actually had inherited hypertrophic cardiomyopathy. The case illustrates the difficulty in diagnosing hypertrophic cardiomyopathy when based solely on the left ventricular gross anatomy.