I seem to recall a newsworthy event some time age where Pfizer put a myocarditis prevention additive into their vaccine.
https://www.fda.gov/media/153447/download
Vaccines and Related Biological Products Advisory Committee Meeting
October 26, 2021
FDA Briefing Document
EUA amendment request for Pfizer-BioNTech COVID-19 Vaccine for use in children 5 through 11 years of age
They added Tris aka Tromethamine to the pediatric dose for 5-11 y/o as a ostensibly as stabilizing agent.
They switched out one buffering solution for another, a common lab solution called TRIS. TRIS just happens to also be used to treat stroke patients. So it’s not exactly something for myocarditis, but it does have to do with reducing the damage of blood clotting disorders.