Acute coronary syndromes (ACS) are characterized by sudden, reduced blood flow to the heart leading to myocardial ischemia, caused by atherosclerotic plaque rupture or erosion, with differing degrees of superimposed thrombosis. The most frequent clinical presentation is intermittent chest pain secondary to coronary artery subocclusion. The absence of electrocardiogram (ECG) abnormalities in a high proportion of patients after pain relief renders the diagnosis difficult. Clinical evaluation is of great importance to distinguish patients with ACS within the very large proportion with chest pain. Troponins play a central role in establishing the diagnosis, however false positive tests are frequent in patients with a low pretest probability and may lead to unnecessary invasive cardiac testing. Prolonged anginal pains of more than 10 minutes are generally secondary to epicardial coronary artery occlusion and associated with ECG abnormalities in a large majority of patients. Patients with persistent ST-elevation should be immediately transported to the hospital for emergent early reperfusion therapy, which reduces myocardial injury and is associated with major improvement of prognosis.