Inclusion Criteria:  Age ≥ 18 years (both Cohort A and B) Received at least one dose of a COVID-19 vaccine in the past 1 month (both Cohort A and B) Developed new clinical signs or symptoms suggestive of myocarditis/myocardial injury within one month of COVID vaccine administration without other known cause (Cohort A, only) Underwent prior cardiac MRI at UHN between 2015-2019 (Cohort B, only)  Exclusion Criteria:  Contraindications to cardiac PET/MRI Current history of COVID-19