Arrhythmogenic right ventricular cardiomyopathy(ARVC) is an inheritant disease with an autosomal dominant mode of transmission with incomplete penetrance and variable expression. Linkage analysis in affected families succeeds in identifying 9 loci determining 9 subtypes of the disease. Genotype phenotype correlation is unclear and the influence of various environmental factors is discussed. Objectives: Genotype phenotype correlation in 2 pairs of monozygotic twins with ARVC and the role of environmental factors are analyzed. Patients and methods: Among 40 pts with ARVC and their 195 relatives there were 2 pairs of monozygotic twins: brothers, age 47 y; and sisters, age 48 y. History, ECG, Holter monitoring, 2D and Doppler Echo, and MRI were analyzed. Results: Twin brothers: ARVC was diagnosed in the proband after the episode of VT with LBBB morphology(enlarged right ventricle, focal hypokinesia of apex, MR evidence of adipose tissue in RV wall). Identical morphology of RV was seen in asymptomatic twin brother. The patient presenting arrhythmia has been rowing for 4 years. Twin sisters: diagnosis was done during family screening. Both were asymptomatic. RV morphology typical for ARVC was found discrete in one of them(bulges adipose tissue in the RV apex); the latter showed changes suggesting RV abnormality(mild segmental dilatation of infundibulum, adipose tissue in a free wall of the RV). No differences in previous viral infections and sports involvement were observed. Conclusions: 1. Clinical picture of ARVC in monozygotic twins is not identical. 2. Strenuous effort may be a factor triggering the arrhythmia in pts with ARVC. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inheritant disease with an autosomal dominant mode of transmission with incomplete penetrance and variable expression. Linkage analysis in affected families succeeds in identifying 9 loci determining 9 subtypes of the disease. Genotype phenotype correlation is unclear and the influence Objectives: Genotype phenotype correlation in 2 pairs of monozygotic twins with ARVC and the role of environmental factors are analyzed. Patients and methods: Among 40 pts with ARVC and their 195 relatives there were 2 pairs of monozygotic twins: Results: Twin brothers: ARVC was diagnosed in the proband after the episode of VT with LBBB morphology (Fig. 2), brothers, age 47 y; and sisters, age 48 y. History, ECG, Holter monitoring, 2D and Doppler Echo, and MRI were analyzed. enlarged right ventricle, focal hypokinesia of apex, MR evidence of adipose tissue in RV wall). Identical morphology of RV was seen in a The patient presenting arrhythmia has been rowing for 4 years. Twin sisters: diagnosis was done during family screening. Both were asymptomatic. RV morphology typical for ARVC was found discrete in one of them (bulges adipose tissue in the RV apex) ; the latter showed changes suggesting RV abnormality (mild segmental dilatation of infundibulum, adipose tissue in a free wall of the RV). No differences in previous viral infections and sports involvement were observed. Conclusions: 1. Clinical picture of ARVC in monozygotic twins is not identical. 2. Strenuous effort may be a factor triggering the arrhythmia in pts with ARVC.