Since May 2021, the Public Health Agency of Canada has been actively monitoring reports of myocarditis and pericarditis following vaccination with COVID-19 mRNA vaccines through passive and active Canadian safety surveillance systems. Available information from international reports, including those from Israel and the United States, indicated that: cases were more commonly reported after the second dose, and symptom onset was typically within several days after vaccination. Cases were mainly among adolescents and young adults and were more often in males compared to females. Cases also typically experienced mild illness, responded well to conservative treatment and rest and had their symptoms improve quickly. In Canada, there have been a small number of reports of pericarditis or myocarditis following vaccination with a COVID-19 mRNA vaccine; however, these are not necessarily related to the vaccine. These reports are not higher than what would be expected in the general population and no clear association has been established between myocarditis or pericarditis and mRNA vaccines.