Histopathological Analysis of Myocarditis

The excised myocardium was kept in formalin and the sections were then embedded in paraffin [19 (link),20 (link),21 (link),22 (link)]. The heart tissue was sectioned and stained with hematoxylin and eosin. The sections were scored for myocarditis as follows in blinded (score 0–4) [13 (link)]. Moreover, the area of inflammatory cells was evaluated using image J (National Institutes of Health, Bethesda, MD, USA), which was shown as the ratio of area of inflammatory cells to that of total area [23 (link)]. Paraffin-embedded heart tissues were also stained with Masson’s trichrome according to the manufacturer’s protocol (Bio-Optica, Milan, Italy).