"Results: 63 patients with a mean age of 15.6 years were included. 92% were male. All had received an mRNA vaccine and, except for one, presented following the

"Results: 63 patients with a mean age of 15.6 years were included. 92% were male. All had received an mRNA vaccine and, except for one, presented following the 2nd dose. Four patients had significant dysrhythmia. 14% had mild left ventricular dysfunction on echocardiography which resolved on discharge. 88% met the diagnostic cardiac magnetic resonance (CMR) Lake Louise criteria for myocarditis. Myocardial injury was more prevalent in comparison to MIS-C patients. None of the patients required inotropic, mechanical, or circulatory support. There were no deaths. Follow up data obtained in 86% of patients, at a mean of 35 days showed resolution of symptoms, arrhythmias, and ventricular dysfunction. Conclusions: Clinical characteristics and early outcomes are similar between the different pediatric age groups. There is evidence of myocardial inflammation and injury following mRNA COVID-19 vaccination as seen on CMR. The hospital course is mild with quick clinical recovery and excellent short-term outcomes. Close follow up and further studies are needed to understand the long-term implications and mechanism of these myocardial tissue changes."