<h4>Aims</h4>We investigated the role of Lgi3-4 proteins in cardiac electrophysiology, with a specific focus on IKur, and their potential contribution to the pathophysiology of atrial fibrillation (AF).<h4>Methods and results</h4>In human atrial tissue and heterologous cells, Lgi3 and Lgi4 interacted with KV1.5 channels. Here, KCNA5 is linked to atrial fibrillation.