Although electrocardiograms were taken from the cesophagus as long ago as 1906 (by Cremer) it was Brown (1936) who first showed the possibilities of the method and made the lead of clinical significance. The cesophagus is in close relation to the left auricle for about 5 cm. below the level of the fifth dorsal vertebra; lower down it is in relationship to the right auricle and the diaphragmatic surface of the ventricles. Thus the cesophageal electrocardiogram can be divided into three sectors. The supra-auricular complexes resemble those in lead VR with negative P waves. At the auricular level P waves are replaced by intrinsicoid deflections which are usually much greater in amplitude than are found in any other lead. At the ventricular level P is positive and the ventricular complexes are like those in lead VF. Between the auricular and ventricular levels there is a transitional zone of varying depth, in which the P waves are becoming peaked, Q waves appear, and