In mutant guinea pig cells, it was shown that decreased inhibition of RyR gating with impaired CaM effect on the CaM-dependent inactivation of ICa,L (i.e. increased ICa,L) may contribute to APD prolongation and that LQTS associated CaM mutations can lead to electrical alternans, a pathological feature of LQTS (Limpitikul et al., 2014). Here, CALM1 is linked to familial long QT syndrome.