Patients with ACS have either acute myocardial infarction (AMI) or UA. For patients with AMI, the reader is referred to the ACCF/AHA Guidelines for the Management of Patients With ST-Elevation Myocardial In- farction (STEMI).2,3 Similarly, for patients with UA that is believed to be due to an acute change in clinical status attributable to an unstable plaque or an abrupt change in supply (eg, coronary occlusion with myocardial supply through collaterals), the reader is referred to the ACCF/AHA Guidelines for the Management of Patients With Unstable Angina/non ST-Elevation Myocardial Infarction (UA/ NSTEMI).4,4a There are, however, patients with UA who can be categorized as low risk and are addressed in this guideline (Table 2). A key premise of this guideline is that once a diagnosis of IHD is established, it is necessary in most patients to assess their risk of subsequent complications, such as AMI or death. Because the approach to diagnosis of suspected IHD and the assessment of risk in a patient with known IHD are concep- tually different and are based on different literature, the writing committee constructed this guideline to address these issues separately. It is recognized, however, that a clinician might select a procedure for a patient with a moderate to high pretest likelihood of IHD to provide information for both diagnosis and risk assessment, whereas in a patient with a low likelihood of IHD, it could be sensible to select a test simply for diagnostic purposes without regard to risk assessment. 