Acute Coronary Syndrome with ST segment elevation requires rapid reperfusion, which is why the timely identification of these conditions, based on the patient's symptoms and the correct interpretation of the EKG, is essential for therapeutic decisions. We report three patients with True Posterior Infarction and their difficult EKG diagnosis. The classic 12-lead EKG method is often not capable of supporting the diagnosis, so we recommend the use of posterior leads and mirror images observing inverted V1-V2-V3 leads on the classic EKG.