For the first few years after the introduction of the string galvanometer into clinical medicine, electrocardiographers devoted most of their attention to the analysis of the cardiac irregularies. This field has been so extensively cultivated that it is approaching exhaustion, and there is an increasing tendency to turn to the significance of abnormalities of the form of the electrocardiographic deflections as a subject of research. The notable contributions which have recently been made to this subject, and the confusion that must result from the conflicting views that have lately been expressed, make it seem advisable to sum up, in a critical way, the present state of our knowledge. The present article is devoted to a careful digest of the literature on those abnormalities of the ventricular complex which indicate disturbances of intraventricular conductivity, and to the presentation of a number of original observations which have a bearing on their interpretation.