Patient had a fib; Heart failure / was coughing really really bad; This spontaneous case was reported by a patient and describes the occurrence of ATRIAL FIBRILLATION (Patient had a fib) and CARDIAC FAILURE (Heart failure / was coughing really really bad) in an 86-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 001A21A and 091L20A) for COVID-19 vaccination.     No Medical History information was reported.   On 21-Jan-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 25-Feb-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. In February 2021, the patient experienced ATRIAL FIBRILLATION (Patient had a fib) (seriousness criteria hospitalization and medically significant) and CARDIAC FAILURE (Heart failure / was coughing really really bad) (seriousness criteria hospitalization and medically significant). At the time of the report, ATRIAL FIBRILLATION (Patient had a fib) and CARDIAC FAILURE (Heart failure / was coughing really really bad) outcome was unknown.            Concomitant medication details were not reported by the reporter. Patient stated that patient was coughing really really bad went to see a doctor who said patient had a fib. Patient received no treatment for the a fib. A week later patient's doctor took her to saw a different doctor who referred patient to a hospital in city who said patient had heart failure. Patient was treated in that hospital for about 6 days. Doctors were just monitoring her blood pressure now & Patient not received any treatment. Patient stated that had no heart related problems previously & has not had a positive Covid test.  It was reported that additional laboratory/diagnostic test blood pressure and were done; however, the outcomes/results of the tests were not provided".  CC: This spontaneous case concerns a 86 year-old female patient, with no medical history reported, who experienced the unexpected, serious (hospitalization, medically significant) Adverse Event of Special Interest of Atrial fibrillation and Cardiac failure, which unknown days after the second dose of mRNA-1273 vaccine administration. The outcome was reported as unknown. It was reported that patient was coughing really bad, then sought consult with a doctor who said patient had atrial fibrillation but no treatment was given. Patient sought consult with another doctor who diagnosed the patient to have heart failure. Patient was admitted and treated at the hospital for about 6 days where his blood pressure was monitored and additional laboratory/diagnostic tests were done; however, the outcomes/results of the tests were not provided. The patient's age could be a confounder for the event Atrial fibrillation. The events Atrial fibrillation and Cardiac failure may be related to each other. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.; Sender's Comments: This spontaneous case concerns a 86 year-old female patient, with no medical history reported, who experienced the unexpected, serious (hospitalization, medically significant) Adverse Event of Special Interest of Atrial fibrillation and Cardiac failure, which unknown days after the second dose of mRNA-1273 vaccine administration. The outcome was reported as unknown. It was reported that patient was coughing really bad, then sought consult with a doctor who said patient had atrial fibrillation but no treatment was given. Patient sought consult with another doctor who diagnosed the patient to have heart failure. Patient was admitted and treated at the hospital for about 6 days where his blood pressure was monitored and additional laboratory/diagnostic tests were done; however, the outcomes/results of the tests were not provided. The patient's age could be a confounder for the event Atrial fibrillation. The events Atrial fibrillation and Cardiac failure may be related to each other. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.