There continues to be considerable variance of opinion regarding the advisability of attempting to restore normal cardiac rhythm by the administration of quinidine in cases of auricular fibrillation. The greatest variance of opinion concerns the type of case in which this should be attempted, the amount of permanent benefit, the size of the dose and the method of administration. PHYSIOLOGIC ACTION OF QUINIDINE Quinidine is an alkaloid of cinchona and is isomeric with quinine.1It is soluble in ninety parts of water and in ten parts of alcohol. It is readily absorbed from the upper portion of the intestinal tract. When given intravenously to animals, it disappears from the blood stream in about five minutes. It is eliminated chiefly by the kidneys. Weiss and Hatcher2found that when quinidine is administered to cats it is almost entirely eliminated in from three to four hours. We found a small