Background; Emerging data have suggested that right ventricular (RV) pacing results in progressive left ventricular (LV) dysfunction. The purpose of this study is to examine the change of LV ejection fraction in the patients who went through dual chamber pacemaker implantation. Methods; From Jan 2005 to Dec 2007, 45 patients who underwent dual chamber pacemaker implantation due to the complete AV block were recruited. QRS width, LVEF, left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter (LVESD), and left atrial volume index (LAVI) were evaluated immediately before pacemaker implantation and around 8 month follow up. LV systolic dysfunction was defined as the LVEF decreased by more than 5% to lower normal (below 55%) compared to the LVEF before the dual chamber pacemaker implantation. Result; Among 45 patients, eight patients had decreased LVEF compared to the LVEF before the dual chamber pacemaker implantation (n=8, 17.8%; male 4, 50% ). The LVEF-preserved group included 37 patients (n=37, 82.2%; male 18, 48.6%). Age, Sex, heart surgery, significant mitral regurgitation and ischemic heart disease were not statistically different between the LVEF-decreased group and the LVEF-preserved group. QRS duration, LAVI, early diastolic mitral annular velocity (E���) and NT-proBNP levels were not statistically different between two groups. And pacing site of RV septum or RV apex did not influence the change of LVEF after the dual chamber pacemaker implantation. Conclusion; After the dual chamber pacemaker implantation, significant number of patients had decreased LVEF compared to the LVEF before the dual chamber pacemaker implantation. And pacing site of RV septum or RV apex did not influence the change of LVEF.