Transmyocardial Temperature Gradient in Dog and Man:

• To account for the negative T wave observed in the left ventricular cavity and the upright T waves in leads taken over the left ventricle, it is assumed that the recovery process may be represented by an electromotive surface with its negative side facing the endocardium and its positive side facing the epicardium. It is paradoxical that in normal hearts this electromotive surface has the same orientation from the standpoint of polarity that a similar model does for the activation process, despite the fact that activation and recovery are opposite processes. This reversed direction of the electromotive surface during recovery is explained on the basis that recovery of muscle units across the ventricular wall is not a uniform process and that there is a more rapid recovery at the epicardial layer compared with the endocardial layer. Previous studies by one of the authors' using measurements of the effective refractory period as an index of the duration of local recovery have shown that, when the T wave as recorded over the left ventricle is positive, recovery is completed more rapidly at the epicardial than at the endocardial surface.