Myopericarditis Following the Third Dose of COVID-19 mRNA Vaccination; The initial case was missing the following minimum criteria: no attribution with suspect drug and event. Upon receipt of follow-up information on (08May2023), this case now contains all required information to be considered valid.  This is a literature report for the following literature source(s).  A 17-year-old male patient with a past medical history of attention deficit hyperactive disease (ADHD) presented to the hospital with a two-day history of substernal chest pain. The pain was dull in nature, intermittent, 8/10 in intensity, non-radiating, and had no aggravating or relieving factors. The pain was associated with intermittent low-grade fever, rigors, chills, and shortness of breath. The patient received a third dose of the Pfizer-BioNTech COVID-19 vaccine within a day before he started to have chest pain. He previously denied having the COVID-19 vaccine and had no complications with the previous two doses of the same vaccine. His presenting vitals were blood pressure of 137/77 mmHg, heart rate of 120 beats per minute, oxygen saturation (SpO2) of 100%, respiratory rate of 18 breaths per minute, and temperature of 100.2° Fahrenheit. His cardiovascular examination did not reveal any murmurs or pericardial rub. Initial electrocardiogram (EKG) showed diffuse ST-elevations. The patient was given high-dose antiplatelets and sublingual nitroglycerine, and cardiac enzymes, complete blood count, and metabolic profile were ordered. The patient's pain subsided; however, a repeat EKG showed sinus tachycardia and an S1Q3T3 pattern. The patient also underwent a CT chest with contrast, which showed no pulmonary embolism, and the lungs were unremarkable. Initial troponins were 0.03 ng/mL and 0.04 ng/mL, which trended up to 3.59 ng/mL within 24 hours of admission, and his C- reactive protein (CRP) was >300 mg/dL. Based on elevated inflammatory serum markers, EKG findings, and troponins, the diagnosis of pericarditis was made. The patient was empirically started on colchicine 0.6 mg twice a day and high-dose aspirin. His workup for the respiratory viral panel, COVID-19 polymerase chain reaction (PCR), and influenza were negative. On day two of admission, he underwent a transthoracic echocardiogram (TTE), which showed a normal left ventricular ejection fraction of 55%, and it showed no wall motion abnormalities or pericardial effusions. On day three of admission, the patient underwent gadolinium-enhanced magnetic resonance imaging, which demonstrated moderate subepicardial and mid-wall delayed enhancement in the inferolateral and basal inferior walls and areas of the adjacent pericardium. These findings were consistent with myopericarditis. As the rest of his workup was negative and because of the recent vaccine, the vaccine was temporally considered the underlying cause of myopericarditis. The patient was discharged on seven days of colchicine and aspirin, and his symptoms completely resolved on day six after the presentation. He has had no other episodes of chest pain on a three-month follow-up and is doing well to date.  No follow-up attempts are possible; information about lot/batch number cannot be obtained. No further information is expected.; Sender's Comments: Based on known drug safety profile, the event myopericarditis is assessed as related to the suspect drug  BNT162B2.  The impact of this report on the benefit/risk profile of the Pfizer product is evaluated as part of Pfizer procedures for safety evaluation, including the review and analysis of aggregate data for adverse events. Any safety concern identified as part of this review, as well as any appropriate action in response, will be promptly notified to RAs, Ethics Committees, and Investigators, as appropriate.