Acute coronary syndrome (ACS) includes both ST (STEMI) and non ST elevation (NSTEMI) MI, and unstable angina. The common pathological process underlying MI involves thrombus formation on top of a complex atheromatous plaque, resulting in partial or complete occlusion of the coronary artery and myocyte necrosis. Unstable angina is defined as ischaemia at rest or on minimal exertion in the absence of myocyte necrosis. Patients with ACS typically present with chest pain; classically central chest pain that radiates to the left arm. Additional symptoms include dyspnoea, nausea, sweating and syncope. Patients can present atypically with gastric symptoms. These are often more common in patients with diabetes, women and the elderly. Clinical risk factors should also be considered when diagnosing ACS as this increases the likelihood of a positive diagnosis. Risk factors include: being older, male, a current or former smoker, known coronary artery disease (CAD), peripheral vascular disease, diabetes, hypercholesterolaemia, renal failure and a family history of CAD. A 12-lead ECG should be performed if possible within 10 minutes of presentation or ideally at first contact with the emergency services. Troponin should be measured on admission and at 12 hours. Ideally high sensitivity troponin should be measured as this has higher negative predictive values for MI and enables earlier detection of acute MI. A chest x-ray should also be carried out to assess for thoracic pathologies. An echocardiogram should be performed during admission in all patients with NSTEMI and STEMI.