In the case of myocarditis after SARS-CoV-2 mRNA vaccination, three main mechanisms by which vaccines might induce hyper-immunity have been proposed: (1) mRNA immune reactivity, (2) antibodies to SARS-CoV-2 spike glycoproteins cross-reacting with myocardial contractile proteins, and (3) hormonal differences [27]. Here, PROS1 is linked to myocarditis.