The diffuse elevation of the ST segment in inferior, anterior and left lateral leads is a major feature differentiating the ECG of acute pericarditis from that associated with acute myocardial ischemia. As discussed earlier, the ST segment elevation occurring after coronary artery occlusion is the result of acute ischemia in the region supplied by the occluded vessel and is localized to the leads which overlie the ischemic zone. There are several other ECG features which help to differentiate the ECG changes of acute pericarditis from those of acute ischemia and these are shown here.