In the past, left ventricular dysfunction in a patient with incessant tachyarrhythmia was considered to be a form of tachyarrhythmia-induced cardiomyopathy [1] whereas patients without frequent tachyarrhythmia were regarded as having preserved cardiac function. However, a number of studies reported patients with Wolff-Parkinson-White syndrome (WPWS) with left ventricular dyssynchrony (LVD) even in the absence of frequent tachyarrhythmia. In these patients, ventricular pre-excitation via the accessory pathway (AP) was considered to be responsible for the dyssynchrony, and the position of the AP in most of the cases was the right side or paraseptal [2,3]. The severity of symptoms in patients with WPWS with LVD (LVD-WPWS) varies; obvious heart failure symptoms are absent in some patients and present in others with severe cardiac dysfunction, which is treated with antiheartfailure drugs, such as diuretics, vasodilators, and beta-blockers, despite their poor efficacy [2,4]. Previous studies showed improvement in LVD in WPWS patients after resynchronization therapy, such as catheter ablation or pharmacologic therapy [2]. Catheter ablation in adults and older children is known to be effective for resynchronization and is the preferred treatment for LVD-WPWS [2]. However, there are relatively few case reports of catheter ablation for LVD-WPWS in underweight children [5], presumably due to the risks involved. Some reports mentioned pharmacological resynchronization in children with WPWS with LVD, but these reports are few. In the