H&E staining reveals no increase in endo-perimysial fibrosis. In (A); representative example of cardiac bundle and perimysial space in human atrial tissue. Circle presents a cardiac bundle, white arrow shows perimysial space, and black arrow shows endomysial space. No significant difference between stages of AF and control SR group in terms of endomysial fibrosis (N = 8, SR; N = 8, ParAF; N = 8, PerAF; N = 5, LS PerAF) (B), and perimysial fibrosis (N = 8, SR; N = 8, ParAF; N = 8, PerAF; N = 5, LS PerAF) (C); respectively, p = 0.77 and p = 0.7542. SR = control group, ParAF = paroxysmal atrial fibrillation, PerAF = persistent atrial fibrillation, LSPerAF = longstanding persistent atrial fibrillation. Statistical tests used: ANOVA.