One result of the recent clinical and experimental investigations of circulatory disturbances and of the clearer recognition of the functions of the heart muscle has been an analysis of the various forms of arrhythmia. Diagnosis, prognosis and treatment alike demand that the physician understand, if possible, the pathological physiology of any given instance of cardiac irregularity. A group of cases in which arrhythmia is not infrequent, and in which the determination of the type of arrhythmia is of considerable importance, is that which includes the irregularities of the pulse occurring during and after infectious diseases. While all textbooks call attention to the fact that the heart may be irregular in almost any of the infectious diseases, there has been little accurate work, based on cardiographic methods, to show what types of irregularity are most often present. This is doubtless due partly to the fact that, with the exception of