Several studies have reported that higher expression of Nav1.5 (Chatelier et al., 2012; Makara et al., 2014), Kir2.1 (Xia et al., 2005; He et al., 2006), Kir3.1, and Kir3.4 (Zhang et al., 2009; Bingen et al., 2013), and lower expression of HCN4 (Macri et al., 2014; Ishikawa et al., 2017) and Cav1.2 (Nakatani et al., 2013; Morishima et al., 2016) can be attributed to the initiation and maintenance of AF. The gene discussed is HCN4; the disease is atrial fibrillation.