Acute coronary syndrome (ACS) is defined as reduced blood flow to the coronary myocardium manifesting as ST-segment elevation myocardial infarction or non–ST-segment elevation ACS, which includes unstable angina and non–ST-segment elevation myocardial infarction. Common risk factors include being at least 65 years of age or a current smoker or having hypertension, diabetes mellitus, hyperlipidemia, a body mass index greater than 25 kg per m², or a family history of premature coronary artery disease. Symptoms most predictive of ACS include chest discomfort that is substernal or spreading to the arms or jaw. However, chest pain that can be reproduced with palpation or varies with breathing or position is less likely to signify ACS. Having a prior abnormal cardiac stress test result indicates increased risk. Electrocardiography changes that predict ACS include ST depression, ST elevation, T-wave inversion, or presence of Q waves. No validated clinical decision tool is available to rule out ACS in the outpatient setting. Elevated troponin levels without ST-segment elevation on electrocardiography suggest non–ST-segment elevation ACS. Patients with ACS should receive coronary angiography with percutaneous or surgical revascularization. Other important management considerations include initiation of dual antiplatelet therapy and parenteral anticoagulation, statin therapy, beta-blocker therapy, and sodium-glucose cotransporter-2 inhibitor therapy. Additional interventions shown to reduce mortality in patients who have had a recent myocardial infarction include smoking cessation, annual influenza vaccination, and cardiac rehabilitation.