Numerator Patients with AMI who have received aspirin within 24 h before or after hospital arrival Denominator All patients with AMI Denominator Exclusions Patients age <18 y Patients who leave against medical advice on day of or day after arrival Patients who die during hospitalization on day of or day after arrival Patients who are on comfort measures/hospice only documented on day of or day after arrival Patients who are transferred to another hospital for inpatient care on day of or day after arrival Patients received in transfer from the inpatient, outpatient, or ED of another facility Patients discharged on day of or day after arrival Denominator Exceptions Documentation of a medical reason for not prescribing aspirin at arrival (eg, aspirin allergy or intolerance, oral anticoagulant therapy as prearrival medication, active bleeding) Patient currently enrolled in a clinical trial precluding the use of aspirin in its protocol (eg, trials of triple versus dual therapy in atrial fibrillation patients) Measurement Period Encounter Sources of Data Medical record or other database (eg, administrative, clinical, registry) Attribution Measure reportable at the facility or provider level Care Setting Inpatient Rationale Coronary heart disease with atherosclerotic plaque disruption (eg, rupture, erosion, ulceration) and superimposed platelet-rich thrombus formation are the main pathophysiological mechanisms causing MI (type 1 or spontaneous MI). Acute occlusion of the coronary artery by the plaque + superimposed thrombus complex results in acute imbalance in myocardial oxygen demand and supply which, when prolonged and unabated, leads to myocardial cell necrosis and infarction. Acute and complete occlusion of the coronary artery usually results in STEMI, which usually presents with persistent ST-elevation on the ECG or as an STEMI equivalent (hyperacute T-wave changes, true posterior MI, multilead ST depression with coexistent ST-elevation in lead aVR, characteristic diagnostic criteria in the setting of LBBB). 