The Third Universal Definition of Myocardial Infarction (MI) was developed by a task force including experts from the European Society of Cardiology (ESC), American College of Cardiology Foundation (ACCF), American Heart Association (AHA), and World Heart Federation (WHF). The definition aims to provide a consistent and precise classification of MI based on clinical, biomarker, and imaging findings. It distinguishes between different types of MI, including spontaneous MI (type 1), MI secondary to ischaemic imbalance (type 2), cardiac death due to MI (type 3), MI associated with revascularization procedures (types 4 and 5), and MI associated with non-cardiac procedures. The definition emphasizes the use of cardiac biomarkers, particularly cardiac troponin (cTn), which is highly specific for myocardial injury. It also incorporates electrocardiogram (ECG) findings and imaging techniques such as echocardiography, radionuclide imaging, magnetic resonance imaging (MRI), and computed tomography (CT) to confirm MI. The document outlines diagnostic criteria for MI, including the presence of elevated cTn levels, ST-segment changes on ECG, and imaging evidence of myocardial injury. It also addresses the challenges of diagnosing MI in patients with non-ischaemic conditions that may mimic MI, such as heart failure, renal failure, and myocarditis. The definition is intended to improve the accuracy of MI diagnosis, facilitate clinical trials, and guide public health policies. The document also discusses the implications of the revised MI definition, including the need for standardized data collection and the importance of distinguishing between incident and recurrent MI events. The third universal definition builds on previous versions, incorporating new data and insights into the pathophysiology of MI and the role of biomarkers and imaging in its diagnosis.The Third Universal Definition of Myocardial Infarction (MI) was developed by a task force including experts from the European Society of Cardiology (ESC), American College of Cardiology Foundation (ACCF), American Heart Association (AHA), and World Heart Federation (WHF). The definition aims to provide a consistent and precise classification of MI based on clinical, biomarker, and imaging findings. It distinguishes between different types of MI, including spontaneous MI (type 1), MI secondary to ischaemic imbalance (type 2), cardiac death due to MI (type 3), MI associated with revascularization procedures (types 4 and 5), and MI associated with non-cardiac procedures. The definition emphasizes the use of cardiac biomarkers, particularly cardiac troponin (cTn), which is highly specific for myocardial injury. It also incorporates electrocardiogram (ECG) findings and imaging techniques such as echocardiography, radionuclide imaging, magnetic resonance imaging (MRI), and computed tomography (CT) to confirm MI. The document outlines diagnostic criteria for MI, including the presence of elevated cTn levels, ST-segment changes on ECG, and imaging evidence of myocardial injury. It also addresses the challenges of diagnosing MI in patients with non-ischaemic conditions that may mimic MI, such as heart failure, renal failure, and myocarditis. The definition is intended to improve the accuracy of MI diagnosis, facilitate clinical trials, and guide public health policies. The document also discusses the implications of the revised MI definition, including the need for standardized data collection and the importance of distinguishing between incident and recurrent MI events. The third universal definition builds on previous versions, incorporating new data and insights into the pathophysiology of MI and the role of biomarkers and imaging in its diagnosis.