Gain-of-function mutations in the pore-forming subunit of I Ks channels, KCNQ1, lead to short QT syndrome (SQTS) and lethal arrhythmias. However, how mutant I Ks channels cause SQTS and the possibility of I Ks -specific pharmacological treatment remain unclear. V141M KCNQ1 is a SQTS associated mutation. We studied its effect on I Ks gating properties and changes in the action potentials (AP) of human ventricular myocytes. Xeno...