Synopsis The diagnosis of most inherited arrhythmia syndromes is based on clinical features and family history. The availability of genetic testing for inherited arrhyth- mia syndromes can: 1) provide opportunity to confirm a suspected clinical diagnosis and sometimes provide prognostic information for the proband and 2) offer cascade screening of potentially affected family mem- bers when a disease-causing mutation is identified in the proband. The yield of genetic testing varies by dis- ease. The verification of pathogenicity of suspected mutations is an evolving field, and exome sequencing has identified an increasing number of variants of un- certain significance in the general population.S4.2.6-1 S4.2.6-5 Genotyping can have therapeutic implications for some arrhythmogenic phenotypes such as long QT syn- drome and Fabry s disease,S4.2.6-6 S4.2.6-9 where a mono- genic pathogenic mutation has been clearly identi- fied, the risk to mutation positive individuals has been extensively studied, and effective therapy relevant to the mutation can be instituted. In other diseases, such as Brugada syndrome, the role of a clear mono- genic disease-causing mutation is less certain, and the genotype does not provide therapeutic or prognostic information for the proband.S4.2.6-5,S4.2.6-10 S4.2.6-12 In ar- rhythmogenic right ventricular cardiomyopathy, some CLINICAL STATEMENTS AND GUIDELINES desmosomal mutation positive individuals do not de- velop disease, indicating that additional mutations and environmental interactions likely influence the clinical development of disease.S4.2.6-13 S4.2.6-16 Importantly, the absence of an identified disease-causing genetic muta- tion does not exclude the presence of disease, and as such, ongoing monitoring and decision-making are done based on the clinical phenotype. 