Objectives: To compare electromechanical ventricular synchrony when pacing from different sites including right ventricular apex pacing (RVAP), right ventricular septum pacing (RVSP), His Bundle pacing (HBP), left bundle branch pacing (LBBP) and RVSP during unipolar pacing from the ring electrode of LBBP lead (RVSPring ) in each patient. Methods: Twenty patients with complete atrioventricular block (AVB) indicated for dual-chamber pacemaker implantation were included. Unipolar pacing at different sites including RVAP, RVSP，HBP，LBBP and RVSPring were successively performed. Pacing characteristics and echocardiogram parameters were compared among intrinsic rhythm and pacing at different sites. Results: Similar to HBP(114.84 ±18.67ms), narrower paced QRSd was found in LBBP(116.15±11.60ms) versus RVSPring(135.11±13.68ms), RVSP(141.75±14.08ms) and RVAP(158.15±21.41ms)(p＜0.001). LBBP showed comparable pacing parameters to RVAP or RVSP and were significantly better than HBP, with maintained cardiac function. TS-12-SD was significantly improved in LBBP(27.00±21.53ms) than RVAP(54.05±34.21ms, p=0.004) and RVSP(47.56±33.26ms, p=0.029) but similar to HBP(37.05±26.24ms, p=0.283) or RVSPring(42.16±26.19ms, p=0.107). Negative values of interventricular mechanical delay(IVMD) were only identified in LBBP(-20.16±18.47ms), significantly different from RVAP(33.68±30.98ms), RVSP (21.68±22.02ms), HBP (4.74±19.04ms) and RVSPring(14.56±26.76ms(all p＜0.001). Using Pearson’s analysis, Sti-LVAT was positively corelated with QRS, IVMD, TS-12-SD, LVEDV and LVESV while a negative relationship was identified for LVEF. Conclusions: Similar to HBP, LBBP achieved better electrical and mechanical left ventricular synchrony than conventional RV pacing. For interventricular synchrony, only LBBP initiated earlier LV activation than RV among these pacing strategies, in consistent with the RBBB pattern of paced QRS during LBBP.