KCND2 and atrial fibrillation: Kv4.2 and Kv4.3, members of the Shal channel subfamily encoded by the KCND2 and KCND3 genes, are channels primarily expressed in the nerves and the heart.[16] In cardiomyocytes, Kv4.2/4.3‐mediated Ito currents are critical for the repolarization of myocardial APs, and a decrease in Ito currents may lead to the prolongation of the AP duration.[17] Loss‐of‐function or gain‐of‐function mutations can cause various cardiac diseases, including lethal atrial fibrillation[18] and ventricular arrhythmias,[19] suggesting that inhibition of Kv4.2/4.3 may cause serious cardiac side effects.