This spontaneous case was reported by a consumer (subsequently medically confirmed) and describes the occurrence of ATRIAL FIBRILLATION (In and Out of Rhythms (Atrial Fibrillation).) in a 78-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 003B21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No medical history was provided by the reporter.  Concomitant products included DESLORATADINE for Allergy, ASA and APIXABAN (ELIQUIS) for Anticoagulant therapy, LOSARTAN and METOPROLOL for Blood pressure, FUROSEMIDE for Diuretic effect, MACROGOL 400, PROPYLENE GLYCOL (SYSTANE) for Dry eye, FLECAINIDE from 14-May-2021 to an unknown date and CLONIDINE for Heart disorder.    On 11-May-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 11-May-2021, the patient experienced ATRIAL FIBRILLATION (In and Out of Rhythms (Atrial Fibrillation).) (seriousness criterion medically significant), HUNGER (Unusual hungry feeling) and BLOOD PRESSURE FLUCTUATION (Fluctuations of Blood Pressure readings). On 15-May-2021, the patient experienced VACCINATION SITE WARMTH (Large, round, red circle, not bright red, warm to touch), VACCINATION SITE ERYTHEMA (Large, round, red circle, not bright red, warm to touch), VACCINATION SITE RASH (Rash in the circle) and VACCINATION SITE SWELLING (Circle 4 inches below the injection site, size of a golf ball). At the time of the report, ATRIAL FIBRILLATION (In and Out of Rhythms (Atrial Fibrillation).), HUNGER (Unusual hungry feeling), BLOOD PRESSURE FLUCTUATION (Fluctuations of Blood Pressure readings), VACCINATION SITE WARMTH (Large, round, red circle, not bright red, warm to touch), VACCINATION SITE ERYTHEMA (Large, round, red circle, not bright red, warm to touch), VACCINATION SITE RASH (Rash in the circle) and VACCINATION SITE SWELLING (Circle 4 inches below the injection site, size of a golf ball) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 12-May-2021, Blood pressure measurement: 104/54 (Inconclusive) At 6:50am, 97/62 (Inconclusive) At 11:40am, 110/62 (Inconclusive) At 2:50pm, 142/89 (Inconclusive) At 8:45pm and 119/69 (Inconclusive) At 10pm. On 12-May-2021, Heart rate: 74 (Inconclusive) At 6:50am, 73 (Inconclusive) At 11:40am, 62 (Inconclusive) At 2:50pm, 109 (Inconclusive) At 8:45pm, 103 (Inconclusive) At 10pm and 97 (Inconclusive) At 2:50pm. On 13-May-2021, Blood pressure measurement: 110/87 (Inconclusive) At 7:12am and 117/76 (Inconclusive) At 8:06am. On 13-May-2021, Heart rate: 104 (Inconclusive) At 7:12am and 101 (Inconclusive) At 8:06am. On 14-May-2021, Blood pressure measurement: 116/80 (Inconclusive) At 7:32am, 129/78 (Inconclusive) At 1:02pm and 169/97 (Inconclusive) At 8:32pm. On 14-May-2021, Heart rate: 99 (Inconclusive) At 7:32am, 102 (Inconclusive) At 1:02pm and 107 (Inconclusive) At 8:32pm. On 15-May-2021, Blood pressure measurement: 140/83 (Inconclusive) At 7:03am, 147/88 (Inconclusive) At 9:19am, 146/96 (Inconclusive) At 4:55pm, 161/95 (Inconclusive) At 8:20pm and 112/83 (Inconclusive) At 10:00pm. On 15-May-2021, Heart rate: 78 (Inconclusive) At 7:03am, 104 (Inconclusive) At 9:19am, 108 (Inconclusive) At 4:55pm, 109 (Inconclusive) At 8:20pm and 95 (Inconclusive) At 10:00pm. On 16-May-2021, Blood pressure measurement: 136/75 (Inconclusive) At 7:03am, 101/67 (Inconclusive) At 9:12am, 101/62 (Inconclusive) At 2:03pm and 127/75 (Inconclusive) At 10:00pm. On 16-May-2021, Heart rate: 101 (Inconclusive) At 7:03am, 104 (Inconclusive) At 9:12am, 90 (Inconclusive) At 2:03pm and 70 (Inconclusive) At 10:00pm. On 17-May-2021, Blood pressure measurement: 139/86 (Inconclusive) At 7:03am. On 17-May-2021, Heart rate: 73 (Inconclusive) At 7:03am.     The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) was unknown.       Treatment information was not provided.  Very limited information regarding the event atrial fibrillation has been provided at this time. For the other events a causal relationship cannot be excluded.  Further information has been requested.; Sender's Comments: Very limited information regarding the event atrial fibrillation has been provided at this time. For the other events a causal relationship cannot be excluded.  Further information has been requested.