heart flutter; This spontaneous case was reported by a consumer and describes the occurrence of CARDIAC FLUTTER (heart flutter) in a male patient of an unknown age who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.     Concurrent medical conditions included Congestive heart failure.   On an unknown date, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On an unknown date, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form and first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On an unknown date, the patient experienced CARDIAC FLUTTER (heart flutter) (seriousness criterion medically significant). At the time of the report, CARDIAC FLUTTER (heart flutter) had resolved.            This spontaneous case was reported by a consumer and describes the occurrence of CARDIAC FLUTTER (heart flutter) in a male patient of an unknown age who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.     Concurrent medical conditions included Congestive heart failure.   On an unknown date, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On an unknown date, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form and first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On an unknown date, the patient experienced CARDIAC FLUTTER (heart flutter) (seriousness criterion medically significant). At the time of the report, CARDIAC FLUTTER (heart flutter) had resolved.            Concomitant medication information was not provided by the reporter.                            Treatment information was not provided by the reporter.  Patient reported that 6 hours after receiving his Moderna booster dose, he experienced heart flutter which lasted 3 hours. Patient has a pre-existing condition of congestive heart failure and wanted to know if this has been reported and if he should receive a second booster.  Company comment: This case concerns a male patient, unknown age, with medical history of congestive heart failure, who experienced the serious unexpected AESI event of cardiac flutter 6 hours after the third (booster) dose of mRNA 1273 Covid-19 vaccine. The patient felt heart flutter that lasted for 3 hours after receiving the booster vaccine. The patient's history of congestive heart failure remains as confounder to the event. The benefit-risk relationship of mRNA 1273 vaccine is not affected by this report.; Sender's Comments: This case concerns a male patient, unknown age, with medical history of congestive heart failure, who experienced the serious unexpected AESI event of cardiac flutter 6 hours after the third (booster) dose of mRNA 1273 Covid-19 vaccine. The patient felt heart flutter that lasted for 3 hours after receiving the booster vaccine. The patient's history of congestive heart failure remains as confounder to the event. The benefit-risk relationship of mRNA 1273 vaccine is not affected by this report.