Myocarditis is a rare complication of COVID-19 vaccination. It affects fewer than 20 people per 1,000,000 COVID-19 vaccinations. 3,5,7 Only the mRNA vaccines (Pfizer-BioNTech and Moderna) have been linked with myocarditis. Myocarditis related to COVID-19 vaccines seems to be caused by the body’s immune response to vaccination.

https://covid19.nih.gov/news-and-stories/covid-19-vaccines-myocarditis