To better understand how compound heterozygous mutations can affect potassium channel function in severe cases of LQTS, all-atom molecular dynamic simulations were carried out, based on the structure for KCNQ1 channel, in activated/open state, reported by Kuenze et al. [13] and based on the structure for hERG reported by Wang et al. [14]. Here, KCNH2 is linked to familial long QT syndrome.