Since Frey1first recommended quinidine sulfate for the treatment of auricular fibrillation, much has been written concerning its merits and disadvantages in this disorder. Various workers2have expressed the opinion that auricular fibrillation is merely a manifestation of the unfavorable progress of otherwise severe heart disease and that in itself it does not materially alter the health of the patient or interfere with cardiac efficiency. Others,3however, have stated the belief that the development of auricular fibrillation adds to the cardiac insufficiency and carries with it certain dangers. The problem is unsettled and warrants further clinical and laboratory investigation. THE EFFECTS OF AURICULAR FIBRILLATION The experimental production of auricular fibrillation in animals reduces the output of the heart by an average of 40 per cent.4It is doubtful that auricular fibrillation causes such a pronounced reduction of function in the already failing heart, but it is