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Background Myocardial infarction (MI) in young adults, has significant health and economic impact for individuals and society at large. While the incidence of MI has fallen over the last 40 years, the rates for MI in the young have been increasing. However, efforts to study this group of patients have been partly hampered by the lack of an agreed definition for prematurity. We sought to examine the definitions of premature MI used by researchers over time and geography.Methods We conducted a scoping review with a literature search in Ovid Medline and the Cochrane Library databases, using key terms such as ‘early’ or ‘premature’ alongside ‘myocardial infarction.’ The search covered all available records up to September 2023. A total of 3,612 eligible studies were identified and screened by two reviewers, of which 136 met the inclusion criteria, specifically focusing on ‘premature MI.’Results Across the 136 studies evaluated, 83 applied the same criteria for both sexes, 45 used sex specific ages with 8 studies including only men or women. We identified 33 different definitions of premature MI, ranging from <35 to <65/male and <70/female, with the most common age cutoffs being ≤45 (14%), ≤40 (10%), and <55/male <65/female (9%).There was notable geographical variation in definition usage, with studies from different countries commonly using different thresholds, such as ≤35 yrs for 3 studies from Greece and <60 yrs for 8 studies from Australia and Mexico. Countries from South and Southeast Asia used lower thresholds compared to the rest of the world.Finally, we noted that the definition of premature (CAD) has changed over time. Before 1990, the study level median age cutoff was ≤52.5 years, decreasing to ≤50 years between 1991–2000, then to ≤45 years from 2001–2010. However, from 2011–2020, it was higher at ≤50 years, and as of 2021, the median cutoff was ≤51.25 yearConclusion We have identified significant variation in the definition of premature MI across studies, with differences observed by country and time period. This may partly reflect ethnic differences and trends in incidence of MI over time. However, the changing and inconsistent use of definitions of prematurity, limits our understanding of this disease phenotype, and the transferability of individual study findings. This work underscores the urgent need to develop consensus for population specific definitions of premature MI, in order to better understand and reduce early onset coronary heart disease globally.Abstract 7-004 Figure 1Graphical demonstration of 33 unique definitions on Premature CADAbstract 7-004 Figure 2Median Premature CAD Definitions by country