The frequency of recording late potentials and their dynamics were studied in 25 patients with coronary heart disease before, during, and after transluminal angioplasty (TAP). Baseline late potentials were observed in 6 (20.7%) cases. During TAP, late potentials were recorded significantly more frequently (48.3%) than the baseline ones (p < 0.03), in 6 (20.7%) patients, late potentials appeared only in arterial dilatation and disappeared after TAP. There was a profound decrease in root-mean-square amplitude of late 40 msec in the QRS complex and an increase in the duration of low-amplitude (less than 40 microV) signals at the end of the QRS complex as compared to the baseline values. In ST-segment elevation, the parameters of the ECG signal-average become deteriorated to a greater degree than those in ST-segment depression.