"One of the strengths of Marriott's Practical Electrocardiography through its more than 50-year history has been its lucid foundation for understanding the basis for ECG interpretation. Again, in this revision, we have attempted to retain the best of the Marriott tradition--emphasis on the concepts required for everyday ECG interpretation and the simplicities, rather than complexities, of the ECG recordings. During preparation of the 9th and 10th editions, Tobin Lim coauthored many of the 11th edition chapters and served as the primary developer of the digital content associated with that edition. Tobin Lim's input continues into this 12th edition, and David Strauss has led even further into the electronic-based interactive learning experiences. More than 30 of the figures that evolved through previous editions have now been converted through the creative expertise of Mark Flanders into animated movies accessed via QR codes imbedded in the book. David has also collaborated with electrocardiographic educators who are especially skilled in e-based education to add interactive video content to many of the 12th edition chapters. Each of the now 24 chapters is divided (as indicated in the table of contents) into discrete, compact "learning units. " Each learning unit begins on a new page to provide blank space for the reader's notes. The purpose of the learning units is to make this book easier to use by allowing the reader to be selective regarding the material to be considered at a particular time. Because the modern student of electrocardiography is primarily oriented to a visual perspective, we have typically begun each page with an illustration"--Provided by publisher.