To analyze the adverse effects of type B ventricular pre-excitation on ventricular wall motion and left ventricular function and its clinical characteristic. The clinical, electrophysiological and echocardiographic characteristics of the 9 cases with type B ventricular pre-excitation before and after ablation seen between March 2011 and March 2013 were analyzed. The patients aged from 3 to 16 years. Five of them were female. Dyschronous left ventricular contraction was demonstrated by M-Mode echocardiography in all of the cases. The basal segments of the interventricular septum turned thin and moved in a manner similar to that of an aneurysm, with typical bulging during end-systole, which was observed in six cases. All patients received successful RFCAs. The locations of the accessory pathways (APs) were the right-sided anteroseptum (n = 2) and the free wall (n = 7). Their physical activities and growth improved greatly in the four cases with coexisting dilated cardiomyopathy (DCM). The echocardiographic data demonstrated that their LV contraction recovered to synchrony shortly after the ablation, LVEF recovered to normal and LVED decreased to almost normal gradually during the follow-up. Overt right-sided APs may have adverse effects on ventricular wall motion and left ventricular function. They can even result in DCM. Dyssynchronous ventricular contraction induced by right-sided overt accessory pathway may be the vital mechanism. Such kinds of cases are indication for ablation with good prognosis.