heart flutter; He felt his heart racing, and it was keeping him up at night; He felt his heart racing, and it was keeping him up at night; It felt like anxiety; little headache; muscle aches; This spontaneous case was reported by a consumer and describes the occurrence of CARDIAC FLUTTER (heart flutter) in a 73-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 050E214) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.    On 14-Sep-2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 15-Sep-2021, the patient experienced HEADACHE (little headache) and MYALGIA (muscle aches). On 16-Sep-2021, the patient experienced SLEEP DISORDER (He felt his heart racing, and it was keeping him up at night), PALPITATIONS (He felt his heart racing, and it was keeping him up at night) and ANXIETY (It felt like anxiety). On 20-Sep-2021, the patient experienced CARDIAC FLUTTER (heart flutter) (seriousness criteria hospitalization and medically significant). The patient was hospitalized from 20-Sep-2021 to 22-Sep-2021 due to CARDIAC FLUTTER. The patient was treated with DILTIAZEM at a dose of 120 mg once a day and METOPROLOL SUCCINATE at a dose of 25 mg twice a day. At the time of the report, CARDIAC FLUTTER (heart flutter), SLEEP DISORDER (He felt his heart racing, and it was keeping him up at night), PALPITATIONS (He felt his heart racing, and it was keeping him up at night), ANXIETY (It felt like anxiety), HEADACHE (little headache) and MYALGIA (muscle aches) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 20-Sep-2021, Heart rate: 170 (High) they admitted him right away with a pulse of 170. They did an ablation had a heart flutter.         No concomitant was provided.  Patient went to the hospital on 20Sep2021, and they admitted him right away with a pulse of 170. They did an ablation, and found a heart flutter.He was discharged after 3 days on 22Sep2021. Patient never had a heart condition. Now feeling better.The patient received his first dose of Moderna COVID19 Vaccine on 05Jan2021 and second dose (lot number 032120A) on 02Feb2021. Consent given for safety to contact the patient and his hospital.  The patient was prescribed some medications for two weeks for his blood pressure: diltiazem ER/CD 120mg once daily and metoprolol succ 25mg twice daily.  Company comment: This case concerns a 73-year-old male patient with no relevant medical history, who experienced the serious unexpected event of Cardiac flutter. The event occurred approximately 7 days after the third dose of Moderna COVID-19 Vaccine.  The rechallenge was not applicable as the event occurred after the third dose. The benefit-risk relationship of Moderna COVID-19 Vaccine is not affected by this report.   This case was linked to MOD-2021-353242, MOD-2021-353234 (Patient Link).; Sender's Comments: This case concerns a 73-year-old male patient with no relevant medical history, who experienced the serious unexpected event of Cardiac flutter. The event occurred approximately 7 days after the third dose of Moderna COVID-19 Vaccine.  The rechallenge was not applicable as the event occurred after the third dose. The benefit-risk relationship of Moderna COVID-19 Vaccine is not affected by this report.