CD44 and atrial fibrillation: An immunohistochemical study revealed that atrial appendage myocardial TCs of patients AF expressed markers of stem cells (CD117+), fibroblast-like cells (vimentin+), hematopoietic stem cells (CD34+) and cell adhesion protein (CD44+), that mediated the adhesion of hematopoietic, fibroblast and glial cells with the extracellular matrix.