The diagnosis acute coronary syndrome includes myocardial infarction together with unstable angina. The definition of the latter diagnosis continues to evolve. Due to widespread clinical application of sensitive markers of myocardial necrosis, including high sensitive cardiac troponin (hscTn) assays, the diagnosis for many newly presenting patients will now be myocardial infarction rather than unstable angina. However, patients presenting with chest pain and very low (< 0.05 ng/L) or undetectable levels of hscTn have been found to be at extremely low risk of development of myocardial infarction and/or death. Consequently, such patients cannot be classified as having unstable angina. A detailed clinical assessment and reasoning will be necessary to establish the true cause of their-often noncardiac symptoms.