CD44 and atrial fibrillation: In 1996, stem cells were found to be present in AF when they were cultivated in the supernatant of rhabdomyosarcoma cell lines and expressed dystrophin as a skeletal muscle protein (40).In 2003, mesenchymal stem cell markers' (Cluster of Differentiation (CD 90), CD105, CD73, CD44) expression of AF-derived cells was confirmed.