The authors have hypothesized that low-level, electrocardiographic changes may accompany transient ischemia induced by percutaneous transluminal coronary angioplasty. Altered repolarization may manifest as subclinical changes in ST-T morphology. Changes in depolarization may manifest as low-amplitude notches and slurs, a phenomenon the authors term abnormal intra-QRS potentials. The initial aim of this study was to characterize changes in high-resolution electrocardiograph signals that might be linked to ischemic involvement of the ventricular myocardium.