Abstract: AIM:To compare the effect of right ventricular outflow tract septum (RVS) pacing and right ventricular apical (RVA) pacing on contraction synchrony, ventricular remodeling and cardiac functions. METHODS: Sixtyone patients (39 males, 22 females) with III atrium ventricular conduction block (AVB) were randomly divided into RVS group (n=33) and RVA group (n=28). The parameters of the pacing leads on implantation and postimplantation and changes of QRS duration of pre and postimplantation were observed. The ventricular synchrony was evaluated by tissue Doppler and left ventricular enddiastolic diameter (LVEDD) and left ventricular ejection fraction (LVEF) were compared between groups. RESULTS: No statistical differences were observed in the pacing parameters between groups (P>005). Postimplantation QRS duration was significantly prolonged in both groups (P<001), especially in the RVA group (P<001). Ts (time to peak systolic velocity) of the left lateral wall to the right wall was (27±14) ms for RVS pacing and (90±22) ms for RVA pacing (P<001). LVEDD of postimplantation significantly increased compared with preimplantation in RVA group ［(54±5) mm vs. (50±4) mm, P<0.05］. LVEF statistically decreased in both groups ［RVS: (0.58±0.14) vs. (0.63±0.09), P<0.01; RVA: (0.51±0.12) vs. (0.64±0.13), P<0.01］. CONCLUSION: RVS pacing achieves a better effect on cardiac contraction synchrony and ventricular remodeling than RVA pacing.