Previous studies have suggested the involvement of the apelin signalling system in cardiac electrophysiology, with plasma apelin levels found to be reduced in atrial fibrillation patients, which can be restored by long-term cardiac resynchronization therapy.39,40 Additionally, apelin peptide has previously been shown to modulate sodium currents in cardiomyocytes, increasing action potential conduction velocity.41,42 The prolongation of voltage signalling in apelin receptor knockdown hESC-CMs suggests dysregulation. The gene discussed is APLNR; the disease is atrial fibrillation.