In this study, we investigated the utility of iPS cells for modelling the long QT syndrome type 3 caused by mutations located in the cytoplasmic loop between membrane-spanning regions S4 and S5 within DI (p.V240M) and in the intracellular linker region between DI and DII (p.R535Q) in the α-subunit of a voltage-gated sodium channel Nav1.5 encoded by a gene SCN5A. Both of these mutations have been previously described as possible LQTS-causing mutations in a genetic screen of 2500 unrelated cases referred for the LQTS genetic test [26]. The gene discussed is SCN5A; the disease is familial long QT syndrome.