For over 20 years, radionuclide ventriculography has been used to localize the atrioventricular accessory pathways associated with Wolff-Parkinson-White syndrome. So far, studies in this field have only included a limited number of patients. Moreover, the phenomenon of successful radiofrequency ablation accessory pathways is not fully understood, and the exact mechanisms leading to disappearance of pre-excitation still have not been worked out. Using scintigraphic imaging techniques, we have assessed the effects of atrioventricular accessory pathways radiofrequency ablation2 and found that the concordance of scintigraphy and endocardial mapping for localizing accessory pathways was broadly confirmed (Fig. 9–8). In addition, the ipsilateral ventricular ejection fraction could be improved following radiofrequency ablation, particularly in patients with left-sided accessory pathways. However, the main finding was that, despite successful ablation of the accessory pathways, unexpected persistence of local ventricular pre-excitation was occasionally unveiled by scintigraphy. The persistence of a zone of premature ventricular contraction as shown by scintigraphy, despite the disappearance of the delta wave on the surface ECG, has never been described. Such a phenomenon may indicate a persisting aborted conduction via the accessory pathway. One must postulate that the atrial insertion of the accessory connection is, at least partly, undamaged. However, it is apparent that the site of anterograde block as a result of ablation occurred near the ventricular interface.