Carolina Bongini and colleagues analyze the prevalence and clinical correlates of atrial fibrillation (AF) in relation to genotype in a large hypertrophic cardiomyopathy(HC) cohort. They concluded that, in patients with HC, genetic testing cannot be used in clinical decision making with regard to management strategies for AF,  genotype is not predictive of onset or severity of AF, and exceptions are represented by rare genes suggesting specific molecular pathways for AF in genetic cardiomyopathies.