The body surface ECG(electrocardiogram) is produced by the electric fields caused by the propagation of action potentials within the myocardial cells. The repolarization phase of the action potential is very sensitive to factors of clinical importance. Therefore, in this paper of the inverse electrocardiography, we studied a method of estimating the uniform action potentials during repolarization phase from the body surface ECG using digital signal identification techniques. The estimated action potential of a normal was similar to that of clinical data in the repolarization phase.