Reduced expressions of plakoglobin and connexin 43 have been reported in the myocardium of patients with arrhythmogenic right ventricular cardiomyopathy (ARVC). However, the relationships between these expression abnormalities and the clinical features of ARVC remain unknown.The expressions of plakoglobin and connexin 43 in myocardial biopsy specimens from 10 patients with confirmed ARVC, and 13 control patients without ARVC (non-ARVC; hypertrophic cardiomyopathy, n = 7; dilated cardiomyopathy, n = 6), were examined by immunostaining to evaluate the relationships between these expressions and the clinical characteristics of ARVC. The ratios of plakoglobin/N-cadherin and of plakoglobin/connexin 43 expressions were significantly lower in the ARVC group than in the control group. Significantly more patients had decreased plakoglobin expression in the ARVC group than in the control group (9/10 versus 7/13; P = 0.0376). Sustained ventricular tachycardia occurred more frequently in patients with ARVC and with decreased expressions of both plakoglobin and connexin 43 than in those with decreased expression of plakoglobin alone (5/5 versus 1/4, P = 0.048).Decreased expressions of both connexin 43 and plakoglobin in the myocardium might be associated with the development of arrhythmia in ARVC.