8 patients were hospitalized with chest pain and were diagnosed with myocarditis. All individuals were healthy males between 21 and 56 years of age. All but 1 patient developed symptoms after their second dose. Systemic symptoms began within 24 hours of vaccine administration in 5 of 8 patients, and chest pain occurred 48 to 96 hours later. Cardiac magnetic resonance imaging revealed patchy delayed gadolinium enhancement consistent with myocarditis in all patients. Subjects presented with symptoms of acute myocarditis 3 days after the second injection and in 5 of 8 patients fever developed one day earlier, supporting the hypothesis that myocarditis could be an adverse reaction related to the mRNA vaccine.