This spontaneous case was reported by a consumer and describes the occurrence of CARDIAC FLUTTER (heart almost felt like fluttered) in a 33-year-old female patient who received mRNA-1273 (Spikevax) (batch no. 302H21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below. No Medical History information was reported. On 12-Feb-2022, the patient received first dose of mRNA-1273 (Spikevax) (Intramuscular) .5 milliliter. On 12-Feb-2022, the patient experienced CARDIAC FLUTTER (heart almost felt like fluttered) (seriousness criterion medically significant), EXTRASYSTOLES (Heart almost felt like skipping), DISCOMFORT (Was so uncomfortable that could not sleep), INSOMNIA (Was so uncomfortable that could not sleep), MYALGIA (Body ache) and HEADACHE (Headache). On an unknown date, the patient experienced CHEST DISCOMFORT (Chest discomfort), MENSTRUATION IRREGULAR (Menstrual period missed), DIZZINESS (Faint feeling) and FATIGUE (Extreme tiredness). The patient was treated with PARACETAMOL (TYLENOL [PARACETAMOL]) for Headache and Muscle ache, at an unspecified dose and frequency. At the time of the report, CARDIAC FLUTTER (heart almost felt like fluttered), CHEST DISCOMFORT (Chest discomfort), EXTRASYSTOLES (Heart almost felt like skipping), DISCOMFORT (Was so uncomfortable that could not sleep), INSOMNIA (Was so uncomfortable that could not sleep), DIZZINESS (Faint feeling), FATIGUE (Extreme tiredness), MYALGIA (Body ache) and HEADACHE (Headache) was resolving and MENSTRUATION IRREGULAR (Menstrual period missed) outcome was unknown. The action taken with mRNA-1273 (Spikevax) (Intramuscular) was unknown. Patient had no history of COVID-19 infection. Patient had no history of myocarditis/pericarditis. Patient had no allergies, has never tested positive for Covid-19 and did not receive any other vaccine within one month prior to Moderna's. She had no chronic illness, patient was not taking any concomitant medication. After a few hours of receiving the vaccine the symptoms started. The patient did not experience symptoms like this before receiving the Moderna COVID-19 vaccine and did not experience similar event in past. Patient was not diagnosed with myocarditis or pericarditis and had not seen a cardiologist or any other HCP. Cardiac lab details like troponin level, ECG or EKG abnormal, cardiac function test abnormal and MRI of the heart performed were not asked. The symptoms were improving but patient was not at her 100%. Company comment: This spontaneous case concerns an 33 year old female patient with no reported medical history, who experienced the unexpected serious (medically significant) AESI Cardiac flutter and unexpected non serious(AESI) of Extrasystoles,  on the same day of receiving the first dose of mRNA-1273 vaccine. Following vaccine administration, she experienced heart flutter, heart skipping, body ache, insomnia, headache, chest discomfort, faint feeling and extreme tiredness. She reportedly missed her menstrual period too. No further information regarding clinical course and management of the event was available from the report. The outcome of the event was recovering. The benefit-risk relationship of mRNA-1273 is not affected by this report. Sender's Comments: This spontaneous case concerns an 33 year old female patient with no reported medical history, who experienced the unexpected serious (medically significant) AESI Cardiac flutter and unexpected non serious(AESI) of Extrasystoles,  on the same day of receiving the first dose of mRNA-1273 vaccine. Following vaccine administration, she experienced heart flutter, heart skipping, body ache, insomnia, headache, chest discomfort, faint feeling and extreme tiredness. She reportedly missed her menstrual period too. No further information regarding clinical course and management of the event was available from the report. The outcome of the event was recovering. The benefit-risk relationship of mRNA-1273 is not affected by this report.