More than 5 million Americans visit hospital emergency departments each year with the complaint of chest pain. Two million patients are admitted to hospitals because of chest pain, but the diagnosis of coronary heart disease is confirmed in only one fourth of them. Acute coronary syndrome represents a clinical syndrome that includes unstable angina, non-Q-wave myocardial infarction and Q-wave myocardial infarction. The goal of management of patients with acute coronary syndrome is to rapidly recognize and manage their cardiac ischemic event, define the risk of myocardial ischemia and recurrent cardiac events, and minimize unnecessary risk to the patient. These decisions can all be made by the use of standard clinical descriptors that include chest pain, the electrocardiogram, and biochemical markers of myocardial injury during and after an acute ischemic episode.