In the method of epicardial potential imaging, the potential distribution on a closed surface bounding the heart is used as the electric generator of the potential field in the electrically passive medium outside the heart, giving rise to the potential field on the body surface. The inverse method involved estimates the full spatio-temporal character of this distribution. Being more proximal to the actual sources inside the myocardial tissue than the body surface potential field, this distribution facilitates the correct interpretation of the underlying electrophysiology. The second method, referred to by some as activation time imaging, uses an equivalent double layer on the heart surface, the delineation of which coincides with the boundary between depolarized cardiac tissue and tissue still at rest.