Atrial fibrillation; Heart go crazy; Bad adverse reaction; Gastrointestinal distress; Upset stomach; She has GERD so this caused indigestion / If she ate a small amount she would get indigestion; There was gas coming out of both ends; This spontaneous case was reported by a consumer and describes the occurrence of ATRIAL FIBRILLATION (Atrial fibrillation) and HEART RATE IRREGULAR (Heart go crazy) in a 68-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 042B21A and 040A21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included GERD. Concomitant products included RABEPRAZOLE SODIUM (ACIPHEX), LEVOTHYROXINE SODIUM (SYNTHROID), LISINOPRIL and CLONAZEPAM (KLONOPIN) for an unknown indication.   On 13-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 10-Apr-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient experienced ATRIAL FIBRILLATION (Atrial fibrillation) (seriousness criteria hospitalization and medically significant), HEART RATE IRREGULAR (Heart go crazy) (seriousness criterion hospitalization), VACCINATION COMPLICATION (Bad adverse reaction), GASTROINTESTINAL DISORDER (Gastrointestinal distress), ABDOMINAL DISCOMFORT (Upset stomach), DYSPEPSIA (She has GERD so this caused indigestion / If she ate a small amount she would get indigestion) and FLATULENCE (There was gas coming out of both ends). The patient was hospitalized for 4 days due to ATRIAL FIBRILLATION and HEART RATE IRREGULAR. At the time of the report, ATRIAL FIBRILLATION (Atrial fibrillation), HEART RATE IRREGULAR (Heart go crazy), VACCINATION COMPLICATION (Bad adverse reaction), GASTROINTESTINAL DISORDER (Gastrointestinal distress), ABDOMINAL DISCOMFORT (Upset stomach) and DYSPEPSIA (She has GERD so this caused indigestion / If she ate a small amount she would get indigestion) outcome was unknown and FLATULENCE (There was gas coming out of both ends) had resolved.            Patient had lot of tests done. She has never had anything like this since.  No treatment information was provided.  This case concerns a 67-year-old female patient with no relevant medical history, who experienced the unexpected serious adverse event of special interest, Atrial Fibrillation and Heart Rate Irregular, the events led to the hospitalization of the patient. The events occurred the same day after receiving the second dose of mRNA-1273 Vaccine. The patient was hospitalized for 4 days due to Atrial Fibrillation and Heart Rate Irregular. The rechallenge is not applicable since no information about the first dose was given. No clinical or treatment details were given. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report.; Sender's Comments: This case concerns a 68-year-old female patient with no relevant medical history, who experienced the unexpected serious adverse event of special interest, Atrial Fibrillation and Heart Rate Irregular, the events led to the hospitalization of the patient. The events occurred the same day after receiving the second dose of mRNA-1273 Vaccine. The patient was hospitalized for 4 days due to Atrial Fibrillation and Heart Rate Irregular. The rechallenge is not applicable since no information about the first dose was given. No clinical or treatment details were given. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report.