Elevation or depression of the ST segment on the body surface electrocardiogram reflect a change in the relationship between the TQ segment and the ST segment rather than a pure shift in the ST segment itself. Thus, the ST segment elevation recorded on the body surface ECG during acute ischemia could result entirely from TQ depression, from ST elevation or from both. In most cases, it is from both and often, depression of the TQ segment is the major component of the apparent ST segment elevation. Similarly, depression of the ST segment on the body surface ECG reflects TQ elevation as well as ST depression.