If the ST segment is not isoelectric, this means that ST segment depression or ST segment elevation is present. ST segment elevation can emerge from the descending R, which is a highly pathological finding and suggestive of an acute myocardial infarction! Alternatively, ST segment elevation can emerge from the ascending S, which may be harmless. However, the finding must be interpreted within the overall clinical context, that is with respect to the patient’s symptoms and medical history. You will learn more about this in the chapter on coronary heart disease and myocardial infarction. The course of the ST segment must also be assessed, that is, you must decide whether it is horizontal, ascending, or descending.