Acute Myocardial Infarction may be defined in several ways according to the pathological, clinical and prognostic features along with different treatment strategies.The most common classification is based on ST-segment elevation on the ECG since this is an excellent predictor of clinical severity: hence, AMI is divided into STEMI (STelevated myocardial infarction) and NSTEMI (Non-ST-elevated myocardial infarction).The former is caused by a complete occlusion of the coronary vessel whereas the latter by a partial occlusion or occlusion in the presence of collateral circulation. The pathological correlate at the myocardial level may be cardiomyocyte necrosis (MI) or, less frequently, myocardial ischemia without cell loss (unstable angina): the two types of MI together with unstable angina make up the group of the Acute Coronary Syndromes (ACS).The clinical spectrum of non-ST-elevation ACS may range from patients free of symptoms at presentation to individuals with ongoing ischemia, electrical or hemodynamic instability or cardiac arrest.