Myocarditis has been reported with COVID-19 but is not clearly recognized as a possible adverse event following COVID-19 vaccination. Objective: To describe myocarditis presenting after COVID-19 vaccination within the Health System. This retrospective case series studied patients within the Health System who experienced myocarditis after COVID-19 vaccination between Jan and Apr2021. Patients who sought care for chest pain following COVID-19 vaccination and were subsequently diagnosed with clinical myocarditis were included. Exposure: Receipt of a messenger RNA (mRNA) COVID-19 vaccine between 01Jan and 30Apr2021. Main outcomes and measures: Clinical diagnosis of myocarditis after COVID-19 vaccination in the absence of other identified causes. Results a total of 23 male patients (median (range) age, 25 (20-51) years presented with acute onset of marked chest pain within 4 days after receipt of an mRNA COVID-19 vaccine. All members were previously healthy with a high level of fitness. Seven received the BNT162b2-mRNA vaccine and 16 received the mRNA-1273 vaccine. A total of 20 patients had symptom onset following the second dose of an appropriately spaced 2-dose series. All patients had significantly elevated cardiac troponin levels. Among 8 patients who underwent cardiac magnetic resonance imaging within the acute phase of illness, all had findings consistent with the clinical diagnosis of myocarditis. Additional testing did not identify other etiologies for myocarditis, including acute COVID-19 and other infections, ischemic injury, or underlying autoimmune conditions. All patients received brief supportive care and were recovered or recovering at the time of this report. They administered more than 2.8 million doses of mRNA COVID-19 vaccine in this period. While the observed number of myocarditis cases was small, the number was higher than expected among male members after a second vaccine dose. Conclusions and relevance: In this case series, myocarditis occurred in previously healthy patients with similar clinical presentations following receipt of an mRNA COVID-19 vaccine. Further surveillance and evaluation of this adverse event following immunization is warranted. Potential for rare vaccine-related adverse events must be considered in the context of the well-established risk of morbidity, including cardiac injury, following COVID-19 infection. An adult male patient received bnt162b2 (PFIZER-BIONTECH COVID-19 VACCINE), via an unspecified route of administration on an unspecified date (Batch/Lot number was not reported) as dose 2, single for covid-19 immunisation. The patient's medical history and concomitant medications were not reported. The patient previously received the first dose of bnt162b2 for covid-19 immunization on an unspecified date. The patient experienced myocarditis in 2021. The patient underwent lab tests and procedures which included echocardiogram findings: unknown results, electrocardiogram findings: unknown results, troponin level: elevated. The patient received brief supportive care and it was unknown if the patient was resolved or resolving at the time of the report. The outcome was unknown.   No follow-up attempts are possible; information about lot/batch number cannot be obtained.; Sender's Comments: A possibly contributory role of BNT162B2 in triggering the onset of myocarditis cannot be fully excluded, considering the temporal relationship.  More immunological and biomolecular evidences would be needed to explore the plausible physiopathologic mechanism