A 55-year-old man was admitted to our hospital for further examination of the abnormalities of chest X-ray and electrocardiogram. He was diagnosed with type B Wolff-Parkinson-White syndrome concomitant with dilated cardiomyopathy. Despite the medical therapy using enalapril and carvedilol for 20 months, his cardiac performance and brain natriuretic peptide (BNP) were not so improved. Because asynchronous septal motion caused by pre-excitation through a right-sided accessory pathway (AP) might deteriorate his cardiac performance, catheter ablation to the AP was performed. Successful procedure after 17 months improved left ventricular (LV) contraction, reduced LV volume, and decreased mitral regurgitation and BNP.