Microscopic findings of cellular hypertrophy from patients with MVS and sinus rhythm (A), MVS and AF in successful maze group (B), and MVS and AF in unsuccessful maze group (C). Microscopic findings of atrial intercellular fibrosis from patients with MVS and sinus rhythm (D), MVS and AF in successful maze group (E), and MVS and AF in unsuccessful maze group (F). MVS: mitral valve surgery; and AF: atrial fibrillation.