This article is a report of the results obtained in a clinical study of the premature contraction, with particular regard to its reaction to the drugs most commonly used in the treatment and study of heart disease. There are in the literature many references to the response of the premature contraction to drugs, as appendixes to studies of cardiac arrhythmias in which attention is given particularly to auricular fibrillation and flutter. This is especially the case in the recent work on the action of quinidine. Edens and Huber1and Wenckebach2reported the action of digitalis on the premature contraction, but recorded impressions rather than the results of carefully controlled experiments. The arrhythmia does not easily lend itself to careful study because of its inconstancy. Patients showing frequent premature contractions in great numbers over long periods of time are not often seen at the hospital. Approximately, one of every five patients