REN and atrial fibrillation: Several profibrotic signaling pathways [2, 15, 16], such as the renin/angiotensin system, transforming growth factor beta (TGFβ) [17], platelet-derived growth factor (PDGF) [18], connective tissue growth factor (CTGF) [19], reactive oxygen species (ROS) [20], inflammation [21, 22], ECM activation (matrix metallopeptidase (MMP), tissue inhibitor of metalloprotease (TIMP)) [23], and apoptosis [24], have been implicated in atrial fibrosis and AF.