Background: Ventricular myocardium near the accessory pathway location is preexcited in patients with WPW syndrome. Preexcitation may result in ventricular dyssynchrony due to its abnormal ventricular activation pattern. However, the relationship between left ventricular dyssynchrony and accessory pathway location has not been elucidated. Methods: Five dogs were studied with following protocol. Through median thoracotomy VDD-type epicardial ventricular pacing with 50-ms AV interval was applied near the AV groove at five different sites in each animal; right anterior, right lateral, left lateral, right posterior, left posterior. Echocardiography was performed to assess maximal difference of radial strain (SRt6) from six mid segments using 2D speckle tracking technique before and during pacing. Results: LV with left lateral preexcitation showed significant LV dyssynchrony comparing to normal condition. (p=0.044, Figure) Peak time of systolic strain was shortened in LV lateral wall and delayed in other segments. Conclusion: Left lateral preexcitation could induce significant LV dyssynchrony. Therefore early intervention such as catheter ablation might be recommended to prevent progression of LV dyssynchrony in patients with WPW syndrome.