Resting membrane potential (RMP) regulates the human atrial action potential (AP). A: Short trains of APs measured at two different RMPs (–85 and –70 mV) in a single human-induced pluripotent stem cell–derived cardiac myocyte (hiPSC-CM), paced at 1 Hz. B, C: Mean data from hiPSC-CMs (N = 18 cells). D: Short trains of APs recorded at 2 RMPs (–85 and –70 mV) in a single primary human right atrial cardiac myocyte, paced at 1 Hz. E: Representative superimposed AP traces recorded from a single primary human right atrial myocyte, paced at 1 Hz. Vertical dashed cursors indicate the end of the stimulus and the action potential amplitude (APA), respectively. Peak dV·dt-1 was measured between these 2 cursors to avoid the stimulus current. F, G: Mean data (N = 14 cells; 6 patients). Data are given as mean ± SEM, 1-way analysis of variance.