Charcot-Marie-Tooth disease (peroneal muscular atrophy) has been reported to cause cardiac arrthymias and conduction disturbances in association with peripheral muscle atrophy. To establish more accurately the frequency of such cardiac disorders in this disease, 68 patients with Charcot-Marie-Tooth disease were evaluated prospectively for evidence of cardiac involvement. Cardiac findings were limited to five patients with conduction defects, two patients with supraventricular tachycardia, two patients with ischemic heart disease, and 20 with mitral valve prolapse. The frequency of each of the abnormal cardiac findings, with the possibly emalities in the population at large. The low incidence of cardiac involvement in patients with Charcot-Marie-Tooth disease may be helpful in distinguishing this disorder from Friedreich's ataxia, an entity that may mimic Charcot-Marie-Tooth disease but that is frequently associated with heart disease.