This is an elegantly simple illustration of normal conduction compared to accessory pathway conduction, as seen in Wolff-Parkinson-White conduction. The image was generously contributed by Christopher Watford, well-know ECG Guru. You can find a collection of illustrations by Christopher at this LINK. PDN files are also available at the link. These will allow you to change the image. Christopher's excellent blog, is My Variables Only Have 6 Letters, and he is a contributer to EMS 12-Lead . Like all content on the ECG Guru website, it is protected by Creative Commons copyright, and is free to use for the purpose of education.