Myocarditis; This literature-non-study case was reported in a literature article and describes the occurrence of MYOCARDITIS (Myocarditis) in a 21-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 prophylaxis.        No Medical History information was reported.    On an unknown date, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, the patient experienced MYOCARDITIS (Myocarditis) (seriousness criterion medically significant). At the time of the report, MYOCARDITIS (Myocarditis) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Activated partial thromboplastin time (23.8-36.2 Second): 32.2 Second. On an unknown date, Atrial pressure: 2 mmHg. On an unknown date, Biopsy: Under electron microscopy revealed normal myocyte morphology and myofibrillary organization. Unusual accumulation of free cell debris and organelles within interstitial areas suggestive of ongoing or prior cellular damage. and biopsy under Light microscopy revealed No significant abnormality. On an unknown date, Blood creatinine: 0.82 mg/dl. On an unknown date, Blood pressure systolic: 133 mmHg. On an unknown date, Body mass index: 21.6 kilogram per square metre. On an unknown date, Body surface area: 1.9 square metre. On an unknown date, C-reactive protein: Less than 1.0 milligram per liter. On an unknown date, Cardiac index: 4.06 litre per minute per square metre. On an unknown date, Echocardiogram: No regional wall-motion abnormality. On an unknown date, Ejection fraction: 64 %. On an unknown date, Electrocardiogram: Normal sinus rhythm, early repolarization.. On an unknown date, Fibrin D dimer: Less than 270 ng/mL. On an unknown date, Haemoglobin: 17.3 g/dL. On an unknown date, Heart rate: 70 beats per minute. On an unknown date, Magnetic resonance imaging heart: late gadolinium enhancement (LGE)in the septal and lateral walls STIR imaging identified focal inflammation in the lateral wall, punctate mid myocardial LGE basal to mid septal and lateral walls, mild RV dilation, small pericardial effusion. On an unknown date, Nasopharyngeal swab: Indeterminant, Positve for spike protein with cycle threshold score of 37.4. On an unknown date, Platelet count (150-400 microliter): 217 microliter. On an unknown date, Platelet factor 4: Negative. On an unknown date, Prothrombin time (11.1-13.7 Second): 13.3 Second. On an unknown date, Pulmonary arterial pressure: 12 mmHg. On an unknown date, Pulmonary arterial wedge pressure: 3 mmHg. On an unknown date, Red blood cell sedimentation rate: 4 mm/hr. On an unknown date, SARS-CoV-2 test: Indeterminant. On an unknown date, White blood cell count: 5.9 10^9/L.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered MYOCARDITIS (Myocarditis) to be related.    Concomitant and treatment medications were not provided.  Patient had symptoms Left sided chest pain and palpitations.      endomyocardial biopsy was provided since vaccination (Vax) 40 days, onset of chest pain was 23 days.  Coronary angiogram was not performed.  The patient did not receive hemodynamic support and an unspecified corticosteroid treatment.  Company comment: This literature non study case concerns a 21 year old male patient with no previous history of myopericarditis or any cardiovascular pathology identified, who experienced the expected, serious (medically significant) AESI of Myocarditis, about 17 days after receiving the third dose with mRNA-1273 vaccine. The patient experienced left sided chest pain with palpitations. His investigations included: Cardiac and inflammatory biomarkers- normal; Echocardiogram- LVEF 64%, no regional wall-motion abnormality; Electrocardiogram- Normal sinus rhythm, early repolarization; Magnetic resonance imaging heart-late gadolinium enhancement(LGE) in the septal and lateral walls; STIR imaging identified focal inflammation in the lateral wall, punctate mid myocardial LGE basal to mid septal and lateral walls, mild RV dilation, small pericardial effusion; Biopsy electron microscopy revealed normal myocyte morphology and myofibrillary organization, unusual accumulation of free cell debris and organelles within interstitial areas suggestive of ongoing or prior cellular damage; Nasopharyngeal swab for COVID 19 RNA-Indeterminant, CoV-2 myocardial RT-PCR (S RNA considered positive)- positive for spike protein with cycle threshold score of 37.4, negative for other 3 regions; Coronary angiogram was not done. The patient did not require any hemodynamic or corticosteroid support. No information on detailed clinical course, treatment, outcome of the event and details pertaining to the previous doses was available in the report. The benefit-risk relationship of mRNA-1273 is not affected by this report.   This case was linked to US-MODERNATX, INC.-MOD-2022-670442, US-MODERNATX, INC.-MOD-2022-670443, US-MODERNATX, INC.-MOD-2022-670433, US-MODERNATX, INC.-MOD-2022-668401 (Linked Report).; Sender's Comments: This literature non study case concerns a 21 year old male patient with no previous history of myopericarditis or any cardiovascular pathology identified, who experienced the expected, serious (medically significant) AESI of Myocarditis, about 17 days after receiving the third dose with mRNA-1273 vaccine. The patient experienced left sided chest pain with palpitations. His investigations included: Cardiac and inflammatory biomarkers- normal; Echocardiogram- LVEF 64%, no regional wall-motion abnormality; Electrocardiogram- Normal sinus rhythm, early repolarization; Magnetic resonance imaging heart-late gadolinium enhancement(LGE) in the septal and lateral walls; STIR imaging identified focal inflammation in the lateral wall, punctate mid myocardial LGE basal to mid septal and lateral walls, mild RV dilation, small pericardial effusion; Biopsy electron microscopy revealed normal myocyte morphology and myofibrillary organization, unusual accumulation of free cell debris and organelles within interstitial areas suggestive of ongoing or prior cellular damage; Nasopharyngeal swab for COVID 19 RNA-Indeterminant, CoV-2 myocardial RT-PCR (S RNA considered positive)- positive for spike protein with cycle threshold score of 37.4, negative for other 3 regions; Coronary angiogram was not done. The patient did not require any hemodynamic or corticosteroid support. No information on detailed clinical course, treatment, outcome of the event and details pertaining to the previous doses was available in the report. The benefit-risk relationship of mRNA-1273 is not affected by this report. US-MODERNATX, INC.-MOD-2022-670443:34-YO-Male US-MODERNATX, INC.-MOD-2022-670433:26-YO-Male US-MODERNATX, INC.-MOD-2022-670442:55-YO-Female US-MODERNATX, INC.-MOD-2022-668401:23-YO-Female