The peak potential values of each cardioelectric wave components detected from the body surface are uniquely presented as a few iso-potential and isochronous contour maps by the electrocardiac peak mapping (EPM) method and apparatus described. The change in the size and the contour of the relevant EPM maps provides a simple, non-invasive, yet sensitive means for clinical diagnosis of at least the following heart diseases:1) the locations and sizes of myocardial infarction (hereafter, MI),2) primary and second cardiomyopathies,3) locations and sizes of "non-Q-wave MI", which can not be diagnosed by conventional electrocardiography, and4) various intracardiac conduction blocks and Wolff-Parkinson-White syndrome,5) various repolarization abnormalities and their quantitative analysis.The EPM apparatus comprises an elastic Waistcoat with embodied special electrodes, signal preprocessors, a multiplexer, a main differential amplifier, and a general purpose computer with appropriate software. The EPM analysis includes the identification of the peak potential and peak time displacement, the contruction of the isopotential and isochronous maps and the diagnosis of heart diseases. The diagnosis is achieved by comparison of the statistically obtained normal values to that of a patient. The complete EPM process can be carried out within ten minutes.