In addition, the increased Ki‐67‐positive cells (Figure 2G), decreased goblet cells (Figure 2H), and reduced tight junction protein expressions (ZO‐1, Occludin, and Claudin‐3) (Figure 2I,J) were observed in FMT‐AM mice, compared with FMT‐AF mice. Here, OCLN is linked to atrial fibrillation.