Myocardial infarction (MI) due to acute obstruction of the left main coronary artery (LMCA) occlusion is a medical emergency, requiring early and prompt diagnosis and revascularization, and unless it is treated, it will frequently result in cardiogenic shock, which has a high fatality rate. Our case focused on a patient, who was transferred to our hospital relatively late due to peculiar ECG. He had acute MI, and was in cardiogenic shock. ECG is the easiest diagnostic method in the early diagnosis of the acute coronary syndromes and in deciding on the early invasive intervention in the high risk group. Before he was sent to us, the patient had an ECG showing right bundle branch block (RBBB) and a AVR ST segment elevation. At the time of the urgent coronary angiography, it was noticed that the LMCA was totally occluded. This case has been presented in order to emphasize that peculiar changes might bring about devastating consequences as in our rare case, showing acute left main coronary artery occlusion, and ST segment elevation only in the AVR on the 12-lead ECG along with upward deflection of ST segment vector might be critical for accurate diagnosis.