Myocarditis following ICB therapy is well described,5 23 24 as is an association with mRNA COVID-19 vaccines.9–12 Cardiomyocytes express high levels of PD-L1 which is upregulated in the context of myocardial injury, serving to abrogate severe myocarditis.25–29 Similarly, PD-L1 expression in the inflamed tumor microenvironment curtails antitumor T cell activity. Here, CD274 is linked to myocarditis.