Figure 1: Light microscopy of post-mortem myocardial specimens without a history of AF (A), paroxysmal AF (B) and persistent AF (C) (Masson’s trichrome stain, magnification x 200) (adapted with permission from (58)). Burden of fibrotic tissue, stained in blue, correlates with duration of AF. D) Diagram detailing normal atrial myocyte bundles and different patterns of fibrotic deposition. In replacement (reparative) fibrosis, degenerating myocytes are replaced by fibrotic tissue within myocyte bundles. Reactive (interstitial) fibrosis involves expansion of the fibrotic tissue in between myocyte bundles. Both forms may coexist within a single atrium.