Acute coronary syndrome (ACS) represents a significant global socioeconomic problem. In the United States, 6-7 million patients present to emergency service annually for chest pain or symptoms of ACS, the diagnosis of ACS being confirmed in 20-25% of these patients.There are two groups of ACS patients, with chest pain as the main and common the presentation that basically has the same pathophysiologic substrate. The groups show differences in electrocardiogram (ECG) changes, or in the presence or absence of ST elevation that distinguishes acute coronary syndrome with ST elevation, or acute myocardial infarction with ST elevation from acute coronary syndrome without ST elevation (ACS-NSTE). Within these groups there are subgroups of patients with acute myocardial infarction without ST elevation (NSTEMI) and patients with unstable angina pectoris (UA). Subgroup distinction between UA and NSTEMI is based on the findings of elevated cardiac markers (troponin). Diagnostic procedures performed at emergency service and coronary unit include history and clinical status, ECG, laboratory testing for cardiac markers and other biochemical parameters, heart and lung x-ray, heart ultrasound, radionuclide methods, and assessment of the risk level (risk score). It should be noted that history data, ECG findings and testing for cardiac markers are of particular importance in setting the diagnosis of ACS. Other useful methods of risk assessment include TIMI degree of risk, which is in general use because of its simplicity, but is less predictive, and the Pursuit and Frisco degree of risk. Regardless of the method used, it is recommended to determine the degree of risk for every patient on admission and at discharge.