HCN4 and Arrhythmia: Based on earlier data from EAM and pacing studies implicating a focal and likely graft-autonomous mechanism underlying these arrhythmias (8, 10, 12, 38), we reasoned that genetic silencing of the pacemaker “funny” current (If) driven by HCN4 would result in more quiescent hPSC-CMs and therefore fewer arrhythmias post-transplantation.