The metabolic, ionic and electrical changes that characterize acute myocardial ischemia are localized to that portion of the myocardium supplied by the involved coronary artery. As a result, a border is created between the normal and the ischemic zone in which there is a transition from the changes occurring in the center of the ischemic zone to the normal myocardium. The metabolic and ionic gradients across this border are accompanied by gradients of electrical change.