With advanced electrophysiological methods evaluation of functional properties and location of accessory pathways has become possible. Multiple pathways may, however, be difficult to outline with regard to localization and electrophysiological properties due to differences in refractoriness and/or fusion of conduction between the pathways. The investigational procedures in patients with multiple accessory pathways are described and discussed in connection with an illustrative patient with three accessory pathways, two of which are Kent's bundles and one most probably a Mahaim's bundle.