Background: We sought to investigate the effect of the left ventricular dyssynchrony (LVdys) on LV torsion (LVtor). Method and Results: Total 25 patients with a delta-wave on electrocardiogram (WPW syndrome) pre-radiofrequency catheter ablation (RFCA) were consecutively enrolled. Echocardiography was performed before and 1 day after RFCA. LV torsion was assessed with 2D speckle tracking technique (frame 60~110/s, mean 87 fps) and LVdys was estimated by a maximal delay among 6 segments at the level of papillary muscle (LVdys index). Results are summarized in Table. No significant changes were observed in BP, HR, LV end-systolic and end-diastolic volumes, LV ejection fraction and paramters reflecting LV diastolic function (mitral inflow, mitral annular velocity and E/E' ratio). LVdys index was significantly increased in 13 Pts who showed LVdys improvement after RFCA (Gr1), as compared with 12 Pts not showing LVdys improvement (Gr2). In Gr1, LVtor was significantly improved (p=0.01), while in Gr2, LVtor was unchanged (p=0.64). A comparison of changes in torsion curve between the 2 groups is displayed in Figure. Conclusions: Despite no alteration in LV ejection fraction, LV torsion can be changed depending on the change in LVdys. Therefore, LVdys exerts a significant effect on LV torsion, irrespective of LV ejection fraction.