Deleterious mutations in KCNQ1 may lead to an autosomal dominant form of long QT syndrome (LQTS) (Romano-Ward) or autosomal recessive form (Jervell and Lange-Nielsen). Both are associated with severe ventricular tachyarrhythmias due to the reduction of the slowly activating delayed rectifier K current (I). Our objective was to investigate the functional consequences of KCNQ1-R562S mutation in an atypical form of KCNQ1-linked LQTS.