1998; Po et al. 2005) and if from the left atrium, then predominantly from the left atrial posterior wall (Sanders et al. 2005; Holmes et al. 2016). Given the crucial role of PITX2 in left–right asymmetry, it is probable that loss of PITX2 in some cases of heritable AF causes incomplete suppression of pacemaker activity in the left heart. This has been shown to be mediated by the loss of Shox2‐silencing and increase in Hcn4 (Wang et al. 2010). The gene discussed is SHOX2; the disease is atrial fibrillation.