On an EKG, ST elevation is an acute myocardial infarction. EKG looks for ST segment elevations in 2 or more contiguous leads. ST elevation only occurs in full-thickness myocardial infarction. One cause of ST segment elevation is the early repolarization of the heart wall due to transmural necrosis. ST segment depression is often seen when myocardial ischemia exists. Ischemia is diminished blood flow to the heart.