ST-segment downward shift is often a manifestation of myocardial ischemia, and is divided into horizontal ST-segment downward shift, ptosis downward shift and upward sloping ST-segment downward shift. The leads of ST-segment downshift can also be used for the localization diagnosis of myocardial ischemia. For example, ST-segment downshift in leads V1-V5 is considered to be myocardial ischemia in the anterior wall of the myocardium, while ST-segment downshift in leads II, III and AVF indicates myocardial ischemia in the inferior wall, and ST-segment downshift in leads V7-V8 indicates ischemia in the posterior wall of the myocardium.