The term acute coronary syndrome (ACS) is used to describe patients who have either unstable angina or an acute myocardial infarction. In ACS, it is believed that the atherosclerotic plaque in the coronary artery ruptures, resulting in platelet aggregation (“clumping”) , thrombus (clot) formation, and vasoconstriction (Fig.40-1). The amount of disruption of the atherosclerotic plaque determines the degree of coronary artery obstruction (blockage) and the specific disease process. The artery has to have at least 40% plaque accumulation before it stars to block blood flow.