This little monograph, which has gone through four editions in six years, is intended for the general practitioner. There have been only a few changes from the third edition and these have concerned themselves chiefly with the section dealing with intraventricular block, which has been recast. The author has taken cognizance of the recent controversy regarding the terminology of bundle branch block, which was precipitated in America, and properly concludes that the evidence for the nomenclature of right and left bundle branch block is not convincing and of but little practical importance. He consequently has made use of the term unilateral bundle branch block of the common and uncommon varieties. He has also substituted for so-called arborization block the term bilateral bundle branch block. As in the past editions, the most instructive part of the monograph is its clear diagrams, which introduce the reader to the fundamental concepts in electrocardiography.