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The universal definition of myocardial infarction (MI) differentiates MI due to oxygen supply/demand mismatch (type 2) from MI due to plaque rupture (type 1) as well as from myocardial injuries of non-ischaemic or multifactorial nature. The purpose of this study was to investigate how often physicians agree in this classification and what factors lead to agreement or disagreement.A total of 1328 patients diagnosed with MI at eight different Swedish hospitals 2011 were included. All patients were retrospectively reclassified into different MI or myocardial injury subtypes by two independent specially trained physicians, strictly adhering to the third universal definition of MI.Overall, there was a moderate interobserver agreement with a kappa coefficient (κ) of 0.55 in this classification. There was substantial agreement when distinguishing type 1 MI (κ: 0.61), compared with moderate agreement when distinguishing type 2 MI (κ: 0.54). In multivariate logistic regression analyses, ST elevation MI (P<0.001), performed coronary angiography (P<0.001) and larger changes in troponin levels (P=0.023) independently made the physicians agree significantly more often, while they disagreed more often with symptoms of dyspnoea (P<0.001), higher systolic blood pressure (P=0.001) and higher C reactive protein levels on admission (P=0.016).Distinguishing MI types is challenging also for trained adjudicators. Although strictly adhering to the third universal definition of MI, differentiation between type 1 MI, type 2 MI and myocardial injury only gave a moderate rate of interobserver agreement. More precise and clinically applicable criteria for the current classification, particularly for type 2 MI diagnosis, are urgently needed.