|Introduction: Long term RV apex pacing can induce left ventricular dyssynchronous contraction and pacemaker induced dyssynchrony is associated with adverse left ventricular remodeling and dsyfunction. But little information has been known about sequential change of ventricular dyssynchrony in patients with pacemaker. Methods: We enrolled 179 patients (male 40.4%, Age 67.7±13.6 yr) underwent permanent pacemaker implantation. Pacing sites were all RV apex. Presence of mechanical interventricular dyssynchrony was evaluated by color coded tissue doppler examination in echocardiography. We checked sequential electrocardiography, laboratory and echocardiographic findings. We analyzed relationship between duration from pacemaker implantation and severity of mechanical dyssynchrony. Results: Mean follow-up time was 725 days. Intraventricular dyssynchrony defined by echocardiographic estimation was not changed significantly (34.4%, 34.9%, p=0.882). Septal to posterior dyssynchrony was not changed significantly (2.1 %, 2.7%, p=0.656). Septal to lateral dyssynchrony was changed significantly (53.0%, 30.0%, p<0.001). Left ventricular ejection fraction was not changed (62.0±7.3 %, 61.8±8.0 %, p=0.722). Tricuspid regurgitation increased mildly (grade 1.04, grade 1.15, p=0.011). QRS width was not different during follow-up (149 msec, 151 msec, p=0.228). Conclusion: Definite LV systolic dysfunction was not verified in patients with RV pacemaker. Pacemaker related tricuspid regurgitation was aggravated as time went by. Paratoxically, septal to lateral dyssynchrony was improved during follow-up. In patients with pacemaker implantation, initial left ventricular dyssynchrony was maintained except septal to lateral dyssynchrony. The lesion why such phenomenon occurred should be evaluated.