The Third Universal Definition of Myocardial Infarction (MI) was developed by a multidisciplinary task force, including experts from the European Society of Cardiology (ESC), American College of Cardiology (ACC), American Heart Association (AHA), and World Heart Federation (WHF). The document aims to provide a consistent and precise definition of MI, which is crucial for clinical trials, observational studies, and quality assurance programs. The definition emphasizes the detection of myocardial necrosis through biochemical markers (e.g., cardiac troponin) and imaging, and differentiates MI from other conditions that may cause myocardial injury, such as spontaneous MI, procedure-related MI, and non-ischemic causes. The definition includes criteria for acute MI, which require evidence of myocardial necrosis in a clinical setting consistent with acute myocardial ischemia. This includes elevated cardiac biomarker levels, such as cardiac troponin (cTn), and specific ECG findings. The document also outlines criteria for prior MI, which may be diagnosed based on pathological Q waves, imaging evidence of viable myocardium loss, or other findings. Additionally, the document addresses various types of MI, including spontaneous MI (type 1), MI due to ischemic imbalance (type 2), cardiac death due to MI (type 3), MI associated with revascularization procedures (types 4 and 5), and MI associated with noncardiac procedures. The document also discusses the role of biomarkers in diagnosing MI, emphasizing the importance of cTn as the preferred biomarker due to its high specificity and sensitivity. It outlines the criteria for cTn elevation, including the 99th percentile upper reference limit (URL), and the importance of considering clinical context when interpreting cTn values. The document also addresses the challenges of diagnosing MI in patients with non-ischemic conditions that may cause elevated cTn levels, such as heart failure, renal failure, or myocarditis. The document provides detailed criteria for diagnosing MI using ECG, including the identification of ST-segment elevation, Q waves, and other ECG changes. It also discusses the role of imaging techniques, such as echocardiography, radionuclide imaging, and magnetic resonance imaging (MRI), in assessing myocardial function, viability, and perfusion. The document emphasizes the importance of imaging in diagnosing MI, particularly in cases where biomarker levels may not be sufficient for a definitive diagnosis. The document also addresses the challenges of diagnosing MI in specific clinical scenarios, such as in patients with left bundle branch block (LBBB), in those with silent MI, and in those with noncardiac procedures. It highlights the importance of considering the clinical context, including the patient's history, symptoms, and biomarker levels, in making a diagnosis of MI. The document concludes with recommendations for the use of imaging and biomarkers in the diagnosis and management of MI, emphasizing theThe Third Universal Definition of Myocardial Infarction (MI) was developed by a multidisciplinary task force, including experts from the European Society of Cardiology (ESC), American College of Cardiology (ACC), American Heart Association (AHA), and World Heart Federation (WHF). The document aims to provide a consistent and precise definition of MI, which is crucial for clinical trials, observational studies, and quality assurance programs. The definition emphasizes the detection of myocardial necrosis through biochemical markers (e.g., cardiac troponin) and imaging, and differentiates MI from other conditions that may cause myocardial injury, such as spontaneous MI, procedure-related MI, and non-ischemic causes. The definition includes criteria for acute MI, which require evidence of myocardial necrosis in a clinical setting consistent with acute myocardial ischemia. This includes elevated cardiac biomarker levels, such as cardiac troponin (cTn), and specific ECG findings. The document also outlines criteria for prior MI, which may be diagnosed based on pathological Q waves, imaging evidence of viable myocardium loss, or other findings. Additionally, the document addresses various types of MI, including spontaneous MI (type 1), MI due to ischemic imbalance (type 2), cardiac death due to MI (type 3), MI associated with revascularization procedures (types 4 and 5), and MI associated with noncardiac procedures. The document also discusses the role of biomarkers in diagnosing MI, emphasizing the importance of cTn as the preferred biomarker due to its high specificity and sensitivity. It outlines the criteria for cTn elevation, including the 99th percentile upper reference limit (URL), and the importance of considering clinical context when interpreting cTn values. The document also addresses the challenges of diagnosing MI in patients with non-ischemic conditions that may cause elevated cTn levels, such as heart failure, renal failure, or myocarditis. The document provides detailed criteria for diagnosing MI using ECG, including the identification of ST-segment elevation, Q waves, and other ECG changes. It also discusses the role of imaging techniques, such as echocardiography, radionuclide imaging, and magnetic resonance imaging (MRI), in assessing myocardial function, viability, and perfusion. The document emphasizes the importance of imaging in diagnosing MI, particularly in cases where biomarker levels may not be sufficient for a definitive diagnosis. The document also addresses the challenges of diagnosing MI in specific clinical scenarios, such as in patients with left bundle branch block (LBBB), in those with silent MI, and in those with noncardiac procedures. It highlights the importance of considering the clinical context, including the patient's history, symptoms, and biomarker levels, in making a diagnosis of MI. The document concludes with recommendations for the use of imaging and biomarkers in the diagnosis and management of MI, emphasizing the