Objective:To restore cardiac autonomic pace function by autologous transplantation and committed differentiation of bone marrow mesenchymal stem cells, and explore the technique for the treatment of sick sinus syndrome. Methods:Mesenchymal stem cells isolated from canine bone marrow were culture-expanded and differentiated in vitro by 5-azacytidine. The models of sick sinus syndrome in canines were established by ablating sinus node with radio-frequency technique. Differentiated mesenchymal stem cells labeled by BrdU were autologously transplanted into sinus node area through direct injection. The effects of autologous transplantation of mesenchymal stem cells on cardiac autonomic pace function in sick sinus syndrome models were evaluated by electrocardiography, pathologic and immunohistochemical staining technique.Results:There was distinct improvement on pace function of sick sinus syndrome animal models while differentiated mesenchymal stem cells were auto-transplanted into sinus node area. Mesenchymal stem cells transplanted in sinus node area were differentiated into similar sinus node cells and endothelial cells in vivo, and established gap junction with native cardiomyocytes. Conclusion:The committed-induced mesenchymal stem cells transplanted into sinus node area can differentiate into analogous sinus node cells and improve pace function in canine sick sinus syndrome models.