Here, we tested LUF7346, one of a series of novel hERG allosteric modulators (Yu et al, 2015, 2016) on a platform of LQT1, JLNS, LQT2, and control isogenic human pluripotent stem cell pairs to (i) rescue the genetic form of LQTS, (ii) reverse drug‐induced LQTS and (iii) correct the combination of genetic and drug‐induced LQTS. This evidence concerns the gene KCNE1 and familial long QT syndrome.