This book presents the authors' concept of the mechanism for the Wolff-Parkinson-White syndrome. That the syndrome may not always be due to an aberrant bundle is not a new idea. Of course, it may still be produced by such a bundle when the latter is present. This syndrome has received much attention, probably considerably more than it deserves. This monograph describes the experience of the authors with their researches and presents their impressions of the mechanism for the Wolff-Parkinson-White syndrome. The monograph should interest those who are concerned about the syndrome.