Can mRNA vaccines cause inflammation of the heart?

Rare cases of inflammation of the heart (myocarditis and pericarditis) have been reported after getting the COVID-19 mRNA vaccines. In Canada, this has occurred at a rate of about 1.7 cases per 100,000 doses of Moderna vaccine and 1.1 cases per 100,000 doses of Pfizer-BioNTech vaccine for older children and adults.

Cases are seen more often after the second dose and in males 12-29 years of age. The rate of cases in males 18-29 years of age after the second dose are about 5 times higher with the Moderna vaccine compared to the Pfizer-BioNTech vaccine. The rate of cases in younger children is much lower. In the US, this occurred at a rate of about 2.7 cases per 1,000,000 doses of Pfizer vaccine in males 5-11 years of age. Rates for children 6 months to less than 5 years of age are unknown at this time. It is expected that cases will be very rare and rates will be lower than the rates for those older than 5 years of age.