The hyperacute T wave changes of acute ischemia/infarction are often difficult to differentiate from the T wave changes of early hyperpotassemia or even from normal T waves. The three sets of leads V2, V3 and V4 shown here illustrate the T waves in these 3 situations. For this reason, the hyperacute T waves of acute ischemia may not be recognized as being due to ischemia unless the ECG reader has a high index of suspicion or has access to a prior ECG that can be used for comparison. Failure to suspect an acute ischemic event when these often subtle T wave changes are present may result in the inappropriate discharge of the patient from the Emergency Department, sometimes with disastrous results.