We studied the effect of exercise-induced ischemia on high-resolution body surface potential maps in the depolarization interval. In particular our aim was to evaluate the effectiveness of selected nine ECG parameters in diagnostics of ischemic heart disease (IHD). The study group consisted of 123 subjects. The distributions of ECG signals averaged in time at rest and at peak exercise were compared. It was observed that for patients with IHD, averaged decreases of QRS amplitude at peak exercise were higher than in the control group and in the group of patients without IHD. IHD was associated also with enlargement of the area on the thorax surface where the decrease in the amplitude and increase in shape changes of the QRS complex were observed. The most effective parameters for the separation of patients with IHD were quantifiers of QRS shape changes. The use of an optimized ECG electrode layout improves the diagnostic value of QRS morphology descriptors.