Recent increase in our knowledge of the basic features involved in ventricular preexcitation has moved it from being a somewhat rare curiosity for which there was no cure to an important medical condition requiring careful therapeutic planning. This review summarizes a body of information concerning mechanisms, various forms of preexcitation, embryologic features, electrophysiology and special testing maneuvers, treatment, prognosis and aviation plus insurance aspects of the syndrome. A new classification of the locations of the Kent bundles in the Wolff-Parkinson-White form of preexcitation is also offered.