Atrial fibrillation; severe chills; severe fatigue; Severe shortness of breath; Panic attack/thought it was a heart attack; Was unable to drive for a while; tachycardia or fast heartbeat; Occasional PACs-premature atrial contraction; Mild Myocarditis when I was in ER; This spontaneous case was reported by a pharmacist and describes the occurrence of ATRIAL FIBRILLATION (Atrial fibrillation), CHILLS (severe chills), FATIGUE (severe fatigue), DYSPNOEA (Severe shortness of breath), PANIC ATTACK (Panic attack/thought it was a heart attack), IMPAIRED DRIVING ABILITY (Was unable to drive for a while), TACHYCARDIA (tachycardia or fast heartbeat), SUPRAVENTRICULAR EXTRASYSTOLES (Occasional PACs-premature atrial contraction) and MYOCARDITIS (Mild Myocarditis when I was in ER) in a 36-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 042B21A and 036A21A) for COVID-19 vaccination.     No Medical History information was reported.   On 19-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 16-Apr-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 22-Apr-2021, the patient experienced ATRIAL FIBRILLATION (Atrial fibrillation) (seriousness criteria hospitalization, disability, medically significant and life threatening), CHILLS (severe chills) (seriousness criteria hospitalization, disability and life threatening), FATIGUE (severe fatigue) (seriousness criteria hospitalization, disability and life threatening), DYSPNOEA (Severe shortness of breath) (seriousness criteria hospitalization, disability and life threatening), PANIC ATTACK (Panic attack/thought it was a heart attack) (seriousness criteria hospitalization, disability and life threatening), IMPAIRED DRIVING ABILITY (Was unable to drive for a while) (seriousness criteria hospitalization, disability and life threatening), TACHYCARDIA (tachycardia or fast heartbeat) (seriousness criteria hospitalization, disability and life threatening), SUPRAVENTRICULAR EXTRASYSTOLES (Occasional PACs-premature atrial contraction) (seriousness criteria hospitalization, disability and life threatening) and MYOCARDITIS (Mild Myocarditis when I was in ER) (seriousness criteria hospitalization, disability, medically significant and life threatening). The patient was treated with ALPRAZOLAM (XANAX) ongoing since an unknown date for Adverse event, at an unspecified dose and frequency and DABIGATRAN ETEXILATE MESILATE (PRADAXA) ongoing since an unknown date for Adverse event, at an unspecified dose and frequency. At the time of the report, ATRIAL FIBRILLATION (Atrial fibrillation), CHILLS (severe chills), FATIGUE (severe fatigue), DYSPNOEA (Severe shortness of breath), PANIC ATTACK (Panic attack/thought it was a heart attack), IMPAIRED DRIVING ABILITY (Was unable to drive for a while), TACHYCARDIA (tachycardia or fast heartbeat), SUPRAVENTRICULAR EXTRASYSTOLES (Occasional PACs-premature atrial contraction) and MYOCARDITIS (Mild Myocarditis when I was in ER) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In 2021, C-reactive protein: high (High) C-reactive protein high. In 2021, Electrocardiogram: normal (normal) normal and irregular (abnormal) irregular. In 2021, Magnetic resonance imaging: abnormal (abnormal) Hospitalization for Atrial fibrillation.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   No Concomitant Medications were provided by the reporter Additional treatment medications included was Cardiac ablation in near future for Atrial fibrillation. Additional lab data included were ECG, Cardiac test, Cardiac enzymes and Troponin level - Within normal limits.  3 days after the second shot, patient had severe shortness of breath, thought it was a heart attack. Followed up with numerous doctors. It was recurring issue. Panic attack was diagnosed at first. Patient had to take 1 month off from work. It was confirmed Atrial fibrillation by cardiologist and electrophysiologist. And hence cardiac ablation is recommended in near future.  Company comment: This case concerns a 36 year-old, male patient with no relevant medical history, who experienced the unexpected events of Atrial fibrillation, chills, fatigue, dyspnoea, panic attack, impaired driving ability, tachycardia, supraventricular extrasystoles and the expected event of myocarditis requiring hospitalization. The events occurred approximately 3 days after the second dose of Spikevax. The rechallenge was not applicable, as the event was reported exclusively after the second dose. The event of myocarditis is consistent with the current understanding of the mechanism of action of the vaccine. The benefit-risk relationship of Spikevax is not affected by this report.; Sender's Comments: This case concerns a 36 year-old, male patient with no relevant medical history, who experienced the unexpected events of Atrial fibrillation, chills, fatigue, dyspnoea, panic attack, impaired driving ability, tachycardia, supraventricular extrasystoles and the expected event of myocarditis requiring hospitalization. The events occurred approximately 3 days after the second dose of Spikevax. The rechallenge was not applicable, as the event was reported exclusively after the second dose. The event of myocarditis is consistent with the current understanding of the mechanism of action of the vaccine. The benefit-risk relationship of Spikevax is not affected by this report.