Abstract: 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.