Introduction : Long term RV 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 relationship between electrical and mechanical dyssynchrony. We aimed to verify implication of paced QRS duration on mechanical dyssynchrony and structural change in long term paced heart. Methods : We enrolled 130 patients (male 41.5%, Age 66.2짹13.0 yr) underwent permanent pacemaker implantation in CNUH. Presence of mechanical interventricular dyssynchrony was evaluated by color coded tissue doppler examination in echocardiography. We checked baseline characteristics, electrocardiography, laboratory and echocardiographic findings. We analyzed relationship between paced QRS duration and presence of mechanical dyssynchrony. And evidence of structural heart remodeling according to paced QRS duration was also assessed. Results : Intraventricular dyssynchrony defined by echocardiographic estimation was observed in 70 patients (53.8%). LV dysfunction was developed in only one patient after long term RV pacing. But patients with increased NT pro-BNP level more than 160 pg/mL were frequent observed (53.6%). There was no statistically significant difference in paced QRS duration according to presence of mechanical dyssynchrony (160.6짹31.5ms with dyssynchrony vs 151.7짹35.1ms without dyssynchrony, p=0.141). Paced QRS duration showed positive correlation with pro-BNP level (r=0.199, p=0.026) but there was no statistically significant relationship between paced QRS duration and LV functional indices such as ejection fraction, Conclusion : Paced QRS duration showed positive correlation with level of NT pro-BNP. But there was no significant relationship between paced QRS duration and mechanical dyssynchrony defined by echocardiographic estimation.