Stomach problems; Pain or irritation on the inner part of his esophagus; Hot flashes; Felt like his heart was beathing very fast; Shortness of breath; Pain or irritation on the inner part of his esophagus; Atrial flutter; Headaches; Flu like symptoms; Feeling druggy; Hurt and soreness on the shoulder; This spontaneous case was reported by a consumer and describes the occurrence of ATRIAL FLUTTER (Atrial flutter) in an 85-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 039b21a, 029k20a and 039k20a) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Ulcer.   On 30-Dec-2020, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 27-Jan-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 23-Aug-2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 23-Aug-2020, the patient experienced INFLUENZA LIKE ILLNESS (Flu like symptoms), FEELING ABNORMAL (Feeling druggy) and VACCINATION SITE PAIN (Hurt and soreness on the shoulder). On an unknown date, the patient experienced ATRIAL FLUTTER (Atrial flutter) (seriousness criterion medically significant), ABDOMINAL DISCOMFORT (Stomach problems), OESOPHAGEAL PAIN (Pain or irritation on the inner part of his esophagus), HOT FLUSH (Hot flashes), HEART RATE INCREASED (Felt like his heart was beating very fast), DYSPNOEA (Shortness of breath), OESOPHAGEAL IRRITATION (Pain or irritation on the inner part of his esophagus) and HEADACHE (Headaches). The patient was treated with PARACETAMOL (TYLENOL) ongoing since an unknown date for Headache, at an unspecified dose and frequency and ESOMEPRAZOLE SODIUM (NEXIUM [ESOMEPRAZOLE SODIUM]) at an unspecified dose and frequency. At the time of the report, ATRIAL FLUTTER (Atrial flutter) was resolving, INFLUENZA LIKE ILLNESS (Flu like symptoms), FEELING ABNORMAL (Feeling druggy), ABDOMINAL DISCOMFORT (Stomach problems), OESOPHAGEAL PAIN (Pain or irritation on the inner part of his esophagus), HOT FLUSH (Hot flashes), HEART RATE INCREASED (Felt like his heart was beathing very fast), DYSPNOEA (Shortness of breath), OESOPHAGEAL IRRITATION (Pain or irritation on the inner part of his esophagus) and VACCINATION SITE PAIN (Hurt and soreness on the shoulder) outcome was unknown and HEADACHE (Headaches) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Electrocardiogram: normal (normal) An EKG was done after the cardioversion and it was fine.         Concomitant medications included blood thinners, blood pressure medication, thyroid medication and cholesterol medication.  On 23 Sep 2021, cardioversion was done in an outpatient clinic.  ECG, cardiac test and cardiac enzymes laboratory test was performed with unknown result.   Most recent FOLLOW-UP information incorporated above includes: On 07-Oct-2021: Follow up received included new events was added.; Sender's Comments: This case concerns a 85 year old male with relevant medical history of Ulcer, who experienced unexpected events of Influenza like illness, feeling abnormal and expected event of vaccination site pain which occurred on the same day after vaccination with the 3rd dose of mRNA (Moderna) , On unknown date after vaccination with the 3rd dose , he experienced unexpected events of  atrial flutter , adominal discomfort, esophageal pain , hot flush , heart rate increased , dyspnea , esophageal irritation  and expected event of headache. The rechallenge for this case is not applicable . The age and history of ulcer are considered confounders for this case ( Aging can cause abnormalities in the heart and may affect the conduction system that may lead to arrhythmias while the history of ulcer may also explain the possible event of abdmominal pain , possible recurrence? ) . The benefit-risk relationship of mRNA-1273 ( Moderna )is not affected by this report.