The purpose of this study was to evaluate the usefulness of tomographic phase analysis in detecting the site of the accessory conduction pathway (ACP) in patients with Wolff-Parkinson-White (WPW) syndrome. Gated emission computed tomography and planar gated blood pool scintigraphy were performed in 20 patients with WPW syndrome, 14 with delta waves and six without delta waves (two intermittent types and four concealed types). The abnormal initial contractions in both planar and tomographic phase images were compared with the sites of ACPs confirmed by epicardial mapping and surgery. The atrioventricular ring was divided into eight segments on each side, and the identification of the initial phase in the segment in which the ACP was located, or that adjacent to it, was considered to be the correct diagnosis. In planar phase analysis, the abnormal initial phase was identified correctly in 8 of 14 patients (57%), whereas in tomographic phase analysis, the site of the ACP was detected in 12 of 14 patients (86%). Tomographic phase analysis can be a helpful adjunctive method in patients with WPW syndrome.