The purpose of this study was to determine the effects of digitalis on the electrocardiograms of children with rheumatic heart disease and signs of heart failure. It has been shown by Cohn and his co-workers1 that an alteration in the size, shape and direction of the T wave of the electrocardiogram is the earliest index of digitalis action. This may take place before disturbances in rhythm and conduction time have occurred and before the patient exhibits any minor toxic manifestations, such as nausea and vomiting. The changes in the electrocardiogram consist essentially in a progressive diminution of the size of the T wave in either one or all three leads, with final inversion of previously upright waves. In cases yielding downwardly directed T waves before the use of digitalis, the drug produces eventually upwardly directed waves. These variations have found ample support in subsequent clinical and experimental observations on