The ECG classification of acute myocardial infarctions has had a profound influence on the treatment of patients with AMI. Deciding whether a patient has ST-segment elevations or a new left bundle branch block or neither of these findings on ECG launches the treating physician down two different treatment pathways: patients with ST-elevation MI need to be assessed for immediate re-perfusion therapy, whereas patients with non-ST-elevation MI are best treated with aggressive medical management without acute reperfusion.