Introduction. Paradoxical or hypokinetic interventricular septal motion has been described in patients with septal or paraseptal accessory pathways. Data regarding nonseptal pathways is limited.Methods and Results. We quantified left ventricular dyssynchrony and function in 16 consecutive children,14.2±3.7years, weighing53 ± 17 kg, prior to and following catheter ablation of bidirectional septal (N=6) and nonseptal (N=10) accessory pathways. Following ablation, the left ventricular ejection fraction increased by4.9±2.1% (P=0.038) from a baseline value of57.0%±7.8%. By tissue Doppler imaging, the interval between QRS onset and peak systolic velocity (Ts) decreased from a median of 33.0 ms to 18.0 ms (P=0.013). The left ventricular ejection fraction increased to a greater extent following catheter ablation of nonseptal (5.9%±2.6%,P=0.023) versus septal (2.5%±4.1%,P=0.461) pathways. The four patients with an ejection fraction <50%, two of whom had left lateral pathways, improved to >50% after ablation. Similarly, the improvement in dyssynchrony was more marked in patients with nonseptal versus septal pathways (difference between septal and lateral wall motion delay before and after ablation20.6±7.1 ms (P=0.015) versus1.4±11.4 ms (P=0.655)).Conclusion. Left ventricular systolic function and dyssynchrony improve after ablation of antegrade-conducting accessory pathways in children, with more pronounced changes noted for nonseptal pathways.