arrhythmias; AFIB; Arm was hurting; Heart pounding at 200 beats per minute; Pain; Feeling hot; Feeling sweaty; Dizziness; This spontaneous case was reported by a consumer and describes the occurrence of ATRIAL FIBRILLATION (AFIB) and ARRHYTHMIA (arrhythmias) in a 44-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 939909, 047B21D and 003B21D) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Acid reflux (oesophageal) and Blood pressure high. Concomitant products included OMEPRAZOLE for Acid reflux (oesophageal), METOPROLOL for Blood pressure high.   On 19-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 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 23-Nov-2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 17-Dec-2021,  after starting mRNA-1273 (Moderna COVID-19 Vaccine), the patient experienced ATRIAL FIBRILLATION (AFIB) (seriousness criteria hospitalization and medically significant). On an unknown date, the patient experienced ARRHYTHMIA (arrhythmias) (seriousness criteria hospitalization and medically significant), PAIN IN EXTREMITY (Arm was hurting), PALPITATIONS (Heart pounding at 200 beats per minute), PAIN (Pain), FEELING HOT (Feeling hot), HYPERHIDROSIS (Feeling sweaty) and DIZZINESS (Dizziness). At the time of the report, ATRIAL FIBRILLATION (AFIB), ARRHYTHMIA (arrhythmias), PALPITATIONS (Heart pounding at 200 beats per minute), PAIN (Pain), FEELING HOT (Feeling hot), HYPERHIDROSIS (Feeling sweaty) and DIZZINESS (Dizziness) outcome was unknown and PAIN IN EXTREMITY (Arm was hurting) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 10-May-2021, Heart rate: irregular heart beat (abnormal) irregular heart beat. On an unknown date, Heart rate: 200 beats per minute (abnormal) 200 beats per minute.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter did not provide any causality assessments.   The patient remarks that when looking at the calendar she realized that both episodes occurred on the same time frame.  The patient stated that she experienced symptoms like this before receiving the Moderna COVID-19 vaccine, on Oct2019. The patient has not been infected with COVID-19. The patient did not have a history of Myocarditis/pericarditis. The patient took unspecified treatment medication to lower the heart rate.   This case was linked to MOD-2021-417305 (Patient Link).; Sender's Comments: This case concerns a 44-year-old, female patient with relevant medical history of hypertension, who experienced the unexpected event of Arrhythmia and was diagnosed with Atrial Fibrillation. The event occurred approximately 25 days after the second dose of mRNA-1273 (Moderna covid-19 vaccine). The rechallenge was not applicable as events occurred after second dose. This patient's underlying medical condition remains a confounder. The benefit-risk relationship of mRNA-1273 (Moderna covid-19 vaccine) is not affected by this report.