This literature-non-study case was reported in a literature article and describes the occurrence of MYOCARDITIS (Myopericarditis) in a 24-year-old male patient who received mRNA-1273 (Spikevax) for COVID-19 vaccination. LITERATURE REFERENCE: Increased interleukin 18-dependent immune responses are associated with myopericarditis after COVID-19 mRNA vaccination. Front Immunol. 2022;13:851620. The patient's past medical history included COVID-19 (mild COVID-19 three months before vaccination). On an unknown date, the patient received first dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced MYOCARDITIS (Myopericarditis). At the time of the report, MYOCARDITIS (Myopericarditis) outcome was unknown. Related. DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Biopsy heart: diffuse cd68+ cell infiltration (abnormal) endomyocardial biopsy revealed diffuse CD68+ cell infiltration. On an unknown date, Cytokine test: increased (High) Th1-type cytokines were highly increased. On an unknown date, Electrocardiogram: abnormal (abnormal) Abnormal. On an unknown date, Interleukin level: increased (High) IL-18 and IL-27 were highly increased. On an unknown date, Troponin I: elevated (High) Elevated.   The action taken with mRNA-1273 (Spikevax) (Unknown) was unknown. For mRNA-1273 (Spikevax) (Unknown), the reporter considered MYOCARDITIS (Myopericarditis) to be related. Patient presented with chest pain. Characterized the immune profile of the patient using multiplex cytokine assay and flow cytometry analysis. In the patient, circulating NK cells and T cells showed an activated phenotype and mRNA profile, and monocytes expressed increased levels of IL-18 and its upstream NLRP3 inflammasome. Collectively, myopericarditis following COVID-19 mRNA vaccination may be associated with increased IL-18- mediated immune responses and cardiotoxicity. Concomitant and Treatment medications were not reported. Company comment: This is a literature non-study case concerning a 24-year-old, male patient with previous medical history of mild COVID-19 three months before vaccination, who experienced the expected, non-serious AESI of Myopericarditis, unknown days after receiving the first dose of mRNA-1273 vaccine. The patient presented with chest pain, elevated troponin I level, and electrocardiogram abnormality. His endomyocardial biopsy revealed diffuseCD68+ cell infiltration. Multiplex cytokine assay and flow cytometry analysis showed circulating NK cells and T cells showed an activated phenotype and mRNA profile, and monocytes expressed increased levels of IL-18 and its upstream NLRP3 inflammasome. Treatment details were not provided in the case. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report. Sender's Comments: This is a literature non-study case concerning a 24-year-old, male patient with previous medical history of mild COVID-19 three months before vaccination, who experienced the expected, non-serious AESI of Myopericarditis, unknown days after receiving the first dose of mRNA-1273 vaccine. The patient presented with chest pain, elevated troponin I level, and electrocardiogram abnormality. His endomyocardial biopsy revealed diffuseCD68+ cell infiltration. Multiplex cytokine assay and flow cytometry analysis showed circulating NK cells and T cells showed an activated phenotype and mRNA profile, and monocytes expressed increased levels of IL-18 and its upstream NLRP3 inflammasome. Treatment details were not provided in the case. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.