A few months after the start of the COVID-19 vaccination campaign, it had already become apparent that there is a connection between the use of COVID-19 mRNA vaccines and very rare cases of heart muscle inflammation (myocarditis), predominantly in young men under the age of 30. In cooperation with the Registry for Children and Adolescents with Suspected Myocarditis (Register für Kinder und Jugendliche mit Verdacht auf Myokarditis, MYKKE Registry), the Paul-Ehrlich-Institut collected and evaluated suspected cases of myocarditis in children and adolescents after a COVID-19 vaccination. The following article presents a summary of the study.