Recent papers published in Cardiovascular Pathology define criteria for the diagnosis of lymphocytic myocarditis in endomyocardial biopsies [1] and also in larger samples of ventricular muscle from surgical or autopsy cases [2]. These guidelines were produced as a joint project by members of the Society for Cardiovascular Pathology (SCVP) and Association for European Cardiovascular Pathology (AECVP) following a consensus meeting in the Seaport area of Boston, USA, thus dubbed the “Seaport criteria”.

The 1984 Dallas criteria [3] are well known, and require myocyte damage for a definite diagnosis of myocarditis. In 2013, the European Society of Cardiology (ESC) published criteria [4] that relied on counting inflammatory cells with immunohistochemistry as an adjunct equal to the need for morphological evidence of myocyte injury. Dallas was criticised for the high bar for a definite diagnosis of myocarditis. ESC criteria seemed more sensitive, but also risked diagnosis of non-specific inflammation as myocarditis when it was part of a systemic response, as was a particular problem during the COVID-19 pandemic. The Seaport criteria take a “mid-Atlantic” view, combining features of both antecedent criteria for a biopsy diagnosis, and extending the criteria to cover surgical and autopsy samples.