Objective Atrioventricular block (AVB) is a common and serious arrhythmia. At present, there is no perfect method of treatment for this kind of arrhythmia. The purpose of this study was to regenerate cardiac atrioventricular conduction by autologous transplantation of bone marrow mesenchymal stem cells (MSCs), and explore new methods for therapy of atrioventricular block. Methods Eleven Mongrel canines were randomized to MSCs transplantation (n=6) or control (n=5) group. The models of permanent and complete AVB in 11 canines were established by ablating His bundle with radiofrequency technique. At 4 weeks after AVB, bone marrow was aspirated from the iliac crest. MSCs were isolated and culture-expanded by means of gradient centrifugal and adherence to growth technique, and differentiated by 5-azacytidine in vitro. Differentiated MSCs (1ml, 1.5×107cells) labeled with BrdU were autotransplanted into His bundle area of canines by direct injection in the experimental group, and 1ml DMEM in the control group. At 1-12 weeks after operation, the effects of autologous MSCs transplantation on AVB models were evaluated by electrocardiogram, pathologic and immunohistochemical staining technique. Results Compared with the control group, there was a distinct improvement in atrioventricular conduction function in the experimental group. MSCs transplanted in His bundle were differentiated into analogous conduction system cells and endothelial cells in vivo, and established gap junction with host cardiomyocytes. Conclusions The committed-induced MSCs transplanted into His bundle area could differentiate into analogous conduction system cells and improve His conduction function in canine AVB models. (J Geriatr Cardiol 2007;4:238-243.) The present of this study was to regenerate cardiac atrioventricular conduction by autologous transplantation of bone marrow mesenchymal stem cells ( MSCs), and explore new methods for therapy of atrioventricular block. Methods Eleven Mongrel canines were randomized to MSCs transplantation (n = 6) or control (n = 5) group. The models of permanent and complete AVB in 11 canines were established by ablating His bundle with radiofrequency technique. At 4 weeks after AVB, bone marrow was aspirated from the iliac crest. MSCs were isolated and culture-expanded by means of gradient centrifugal and adherence to growth technique, and differentiated by 5-azacytidine in vitro. Differentiated MSCs (1 ml, 1.5 x 107 cells) labeled with BrdU were autotransplanted into His bundle area of ​​canines by direct injection in the experimental group, and 1 ml DMEM i At control cycles of 1 to 12 weeks after operation, the effects of autologous MSCs transplantation on AVB models by evaluated electrocardiogram, pathologic and immunohistochemical staining techniques. Results with the control group, there was a distinct improvement in atrioventricular conduction function in the experimental group. MSCs transplanted into His bundle were differentiated into analogous conduction system cells and endothelial cells in vivo, and established gap junction with host cardiomyocytes. conclusions The committed-induced MSCs transplanted into His bundle area could differentiate into analogous conduction system cells and improve His conduction function in canine AVB models. (J Geriatr Cardiol 2007; 4: 238-243.)