Chest pain is a common reason for presentation at hospital emergency departments, where physicians are faced with the problem of quickly and accurately distinguishing between patients with acute myocardial infarction (MI), unstable angina, and pain of non-cardiac origin. In acute MI, the initial electrocardiogram (ECG) may show ST elevation in only 50% of cases, and a wide variety of ECG appearances are all consistent with a diagnosis of unstable angina. Serum markers of myocardial injury, particularly troponin-T or -I, may be helpful but are time-sensitive. In patients who are ruled out for acute MI, myocardial perfusion imaging offers additional diagnostic and risk stratification information with a normal result possibly allowing patients to be discharged home, while an abnormal result offers good predictive value for further events. Patients with acute MI or unstable angina should start specific treatment immediately. Thrombolysis is not indicated in unstable angina or non-Q-wave RAI, but it has recently become apparent that early treatment with the glycoprotein (GP) IIb/IIIa receptor inhibitor eptifibatide reduces mortality and morbidity in these patients.