The 12-lead electrocardiogram (ECG) remains the cornerstone of prompt diagnosis of STEMI; Furthermore, the 12-lead ECG provides the primary indication for emergent reperfuison therapy in the STEMI patient. In certain cases, a patient’s ECG can resemble STEMI yet manifest ST-segment elevation from a non-coronary-based syndrome; these entities are termed the STEMI mimics and include benign early repolarization, acute pericarditis, and left ventricular aneurysm, to name only a few. In other situations, the patient’s ECG makes it difficult or impossible to determine whether STEMI is present, the so-called STEMI confounders and include left bundle branch block pattern, left ventricular hypertrophypattern, and the ventricular paced pattern. The goal with STEMI mimics and confounders is to maximize rapid, accurate diagnosis while avoiding delays in treatment of alternative causes of ST-segment elevation.