Fifth Universal Definition of Myocardial Infarction (2026): On Behalf of the Joint European Society of Cardiology (ESC)/American College of Cardiology (ACC)/American Heart Association (AHA)/World Heart Federation (WHF) Task Force for the Universal Definition of Myocardial Infarction

The Fifth Universal Definition of Myocardial Infarction (UDMI) updates the classification to better reflect underlying pathophysiology, align with clinical evaluation of patients, and incorporate objective diagnostic criteria. This classification recognizes that myocardial infarction occurs in three clinical settings. First, myocardial infarction can arise spontaneously due to an acute coronary pathology (primary myocardial infarction). While most presentations are due to atherothrombosis, alternative coronary pathologies can be identified using coronary imaging and functional testing. Second, myocardial infarction may result from another acute condition causing oxygen supply–demand imbalance (secondary myocardial infarction). Here, objective criteria are proposed to guide the use of cardiac and invasive or non-invasive coronary imaging, promoting consistent diagnosis and informing treatment. Third, myocardial infarction may occur as a complication of percutaneous or surgical cardiac procedures (procedure-related myocardial infarction). The diagnosis of procedure-related myocardial infarction does not rely on cardiac biomarker thresholds and is comparable for percutaneous and surgical procedures. In each of these three settings, guidance is provided on the interpretation of symptoms and signs of myocardial ischemia, cardiac biomarkers, and imaging. Alignment of the classification of myocardial infarction with International Disease Classification (ICD)-11 codes, its distinction from myocardial injury, and implications for patients, public health, and research are discussed. It is anticipated that adoption of the classification in practice and research will ensure the diagnosis of myocardial infarction is meaningful for patients and clinicians with clear implications for care across healthcare settings.