This seems paradoxical, but AF has been proposed to arise from (i) a prolonged effective refractory period, which increases the likelihood of early afterdepolarization arrhythmias, which could arise from loss-of-function Kv1.5 mutants34 or (ii) a reduced effective refractory period, increasing the likelihood of re-entrant arrhythmias, which could arise from gain-of-function Kv1.5 mutants32. Here, KCNA5 is linked to atrial fibrillation.