Objective To investigate the applicable value of tissue synchronization imaging (TSI)by real-time thriplane echocardiography (RT3PE)in cardiac resynchronization therapy (CRT).Methods Twenty-four patients with heart failure scheduled for CRT and 24 healthy controls were enrolled.Two dimensional echocardiography was performed to get the left ventricular internal diameter at end-diastole and end-systole(LVIDd,LVIDs ),left ventricular ejection fraction (LVEF ),velocity time integral of left ventricular outflow tract flow (VTILVOT ).The RT3PE TSI was performed to measure the time to peak systolic velocities(Tp)of left ventricle basal and middle segments(12 segments),software will automatically calculate the maximal difierence (12-Tp-DIF)and standard deviation (12-Tp-SD)of Tp in 12 segment. Identity the segment where wall motion most delay and to guide electrode placement.AV and VV interval optimization were performed under guidance of TSI after 1 month of CRT.Results In before CRT,after CRT,after optimization and control group,LVIDd,Tp,LVIDs,12-Tp-DIF and 12-Tp-SD were decreased in the order,LVEF and VTILVOT were increased in the order.There were significant difference between the groups(all P < 0.05 ).TSI showed that left ventricular systolic dyssynchrony was present in all patients before CRT.The most delay segment and electrode location was consistent.There were close correlation between 12-Tp-DIF and LVEF (r =-0.70,P =0.000),between 12-Tp-SD and LVEF(r =-0.73,P =0.000).Conclusions Left ventricular systolic synchronicity can be evaluated accurately and intuitively using TSI by RT3PE.It has important clinical significance in prospectively select patients for CRT,help to guide electrode placement and to optimize device programming.