Objective：To observe the protective effect of left bundle branch pacing(LBBP)on cardiac function in patients with ventricular pacing dependency and explore the possible mechanism. Methods：A total of 42 patients undergoing permanent cardiac pacemaker implantation due to atrioventricular block or slow heart rate of atrial fibrillation in Suzhou Municipal Hospital from August 2018 to February 2021 were enrolled in this study. According to the pacing site，the patients were divided into LBBP group(19)and right ventricular pacing(RVP)group(23)including 11 of right ventricular outflow tract septal pacing(RVSP)and 12 of right ventricular apical pacing(RVAP).The preoperative and postoperative QRS duration(QRSd)，left ventricular ejection fraction(LVEF)，left ventricular end diastolic diameter(LVEDD)and end systolic diameter(LVESD)were compared between groups. At the end of follow- up，real-time three-dimensional ultrasound was used to assess inter-ventricular and intra-ventricular mechanical synchrony.Results： The mean follow-up time was(22.27±10.28)months. LVEF in LBBP group had no significant change before and after operation，LVEF in RVP group was significantly decreased[(54.09±9.27)% vs(. 58.94±10.01)%，P=0.011]. LVEDD and LVESD in the two groups had no significant change after operation. The baseline QRSd were similar between two groups. The paced QRSd in LBBP group was similar with the baseline QRSd，but significantly narrower than that in RVP group[(115.79±14.27)ms vs(. 147.83±19.76)ms，P=0.000]. Left ventricular activation time(LVAT)in LBBP group was significantly shorter than that in RVSP patients[(65.25±19.79)ms vs(. 80.91± 10.44)ms，P=0.003]. Inter-ventricular mechanical delay(IVMD)was significantly different between LBBP and RVP groups[(-12.66± 15.99)ms vs.(15.13±19.12)ms，P=0.000]. Standard deviation of time to minimum systolic volume in 16 segments of left ventricle (Tmsv16- SD)and Tmsv16- SD after heart rate correction(Tmsv16- SD/R -R)in LBBP group were smaller than those in RVP group [(23.35±9.34)ms vs(. 37.31±22.95)ms，P=0.021]，[(2.65±0.92)ms vs(. 4.04±2.48)ms，P=0.030]. Correlation analysis showed that QRSd，Tmsv16-SD，Tmsv16-SD/R-R were significantly negatively correlated with LVEF(P ＜ 0.05)，and significantly positively correlated with LVEDD and LVESD(P ＜ 0.05). Conclusion：LBBP can protect cardiac function better than RVP in patients with ventricular pacing dependency，which may be related to LBBP’s ability to better maintain cardiacelectrical and mechanical synchrony.