Background: Dual-chamber pacing (DDD)is believed to have an advantage over single-chamber pacing (VVI). The aim of the study was to determine whether patients can have significant myocardial functional benefit from dual-chamber pacing compared with single-chamber pacing. Methods: This study included 13 patients with DDD) and 24 patients with VVI at least 12 months. Transthoracic 2D echocardiography, tissue synchronization imaging(TSI), and strain echocardiography were performed to determine the chamber size, standard deviation of the time to peak systolic velocity in ejection period(SD-Ts) among the 12 LV segments, myocardial performance index, and global LV strain, LA diameter, LA volume index and mitral inflow parameters. Longitudinal peak strain and strain rate were obtained from 2 different areas of the basal LA free wall and the inter-atrial septum in the apical 4 chamber view using the tissue Doppler strain. Results: Although there was no significant difference in the myocardial performance index and mitral inflow parameters, the global LV strain and peak systolic LA strain were significantly lower in VVI than DDD indicating deteriorated LV and LA function with VVI (Table). In addition, there was significant difference in the intraventricular delays of SD-Ts (dyssynchrony index) in favor of DDD (with VVI 52.914.7 ms vs. DDD 37.715.7 ms; p=0.009). Interestingly, the peak LA strain showed strong negative correlation with the duration of pacemaker inserted period (r=-0.42, p=0.028) Conclusions: Single-chamber pacing was associated with increased LV dyssynchrony and impared LV and LA function compared with dual-chamber pacing. Dual-chamber pacing would have benefit on cardiac function than single-chamber pacing in long-term follow-up.