It is useful to construct the epicardial isopotential mapping (the Ep Map) from the body surface isopotential mapping (the Body Map) for clinical diagnosis of cardiac disease, even though there are many unsolved problems in using the inverse solution. Yamashita et al. carried out this solution by using the finite element technique. In the present study, the clinical value of that method has been investigated in cases of myocardial infarction. The Ep Maps at 20, 25 and 30 msec. from the beginning of the QRS complex were obtained from the Body Map at the same time by using that method; the infarcted areas on the Ep Map were determined by using Toyama's method which was reported in a previous study. The infarcted area at 30 msec. on the Ep Map was located at the anterior wall along the ventricular septum in anterior infarction and at the posterior wall of the left ventricle in inferoposterior infarction. Patients were independently examined with the scintigram with thallium-201 and the infarcted area was coincident to the location of the abnormal findings of the scintigram. Moreover, the size of the infarcted area on the Ep Map and the size of the abnormal findings of the scintigram were parallel in most cases except one.