A rare case of congenital hypoplasia of the right ventricular myocardium ("Parchment Right Ventricle" or Uhl's disease) diagnosed by angiocardiography is presented. The predominant clinical feature was recurrent paroxysms of severe arrhythmias which could be controlled only by electric shock. Right heart failure was also present. After a follow-up period of 8 years, the patient, now 27 years old, on diuretic and antiarrhythmic treatment, is well. The literature on Uhl's disease is reviewed and classified into two clinical types; a fatal infantile type in which extreme hypoplasia is present, and a milder adult type in which the anatomical lesion is usually more limited. In the infantile type intractable heart failure was invariably present; in the adult type severe arrhythmias often constituted the major clinical problem. Some of the difficulties in diagnosis and treatment are emphasized.