Atrial fibrillation is the commonest sustained arrhythmia in the general population, and is associated with other cardiovascular diseases and morbidity.111 Apelin is involved in regulation of cardiomyocyte electrophysiology, acting on several ion channels to shorten the action potential and increase conduction velocity.99,112 Slowed myocardial conduction velocity is associated with an increased risk of arrhythmia,113 and apelin knockout mice have reduced atrial conduction velocities.114. The gene discussed is APLN; the disease is cardiac arrhythmia.