Presents some preliminary data suggesting that acute myocardial ischemia may be uniquely detectable in the QRS complex of the high resolution ECG. It is hypothesized that acute ischemia may create functional block, leading to ischemically-altered ventricular activation patterns. The study assessed four subjects undergoing elective PTCA. A continuous 12-lead HRECG was recorded and analyzed in 1-minute segments. Changes in the HRECG between the preinflation, artery-occluded and post-deflation states took the form of abnormal intra-QRS potentials. These data were trended and compared to severity estimates of ischemia obtained during balloon occlusion by tomographic scintigraphy. The abnormal QRS potentials may predict the overall degree of myocardial ischemia and exhibit forms which are specific to the artery occluded.