Introduction : Preexcitation is associated with asynchronous interventricular contraction in left ventricle(LV). We investigated the different extent of LV dyssynchrony depending on the accessory pathway location and the effect of RF catheter ablation(RFCA) on dyssnchronous parameteters using 2D speckle tracking echocardiography. Methods : Consecutive 25 patients(16 males, 30.2짹13.1 years) with WPW syndrome who underwent successful RFCA were enrolled. Echocardiography was performed to assess standard deviation of time to peak radial strains from six mid segments(SRt6s) using 2D speckle tracking technique before and after RFCA. Results : Left lateral preexcitation showed more significant LV dyssynchrony comparing to other accessory pathway locations. After RFCA, all patients��� dyssynchrony parameters were normalized. ( 117.4 짹53.6 vs. 19.8짹16.3 ms, pre-vs. post-RFCA, P<0.001, as Figure) Conclusion: LV dyssynchrony was more prominent in patients with left lateral accessory pathway. Intraventricular dyssynchrony was normalized after RFCA in all patients.