feels something very heavy on her; Arrhythmia/ her heart rate went up and down; This spontaneous case was reported by a consumer and describes the occurrence of ARRHYTHMIA (Arrhythmia/ her heart rate went up and down) in a 68-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 024c21a and 050c21a) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Graves' disease (Thyroid removed) and Thyroidectomy. Concurrent medical conditions included Drug allergy (allergy to tapazole). Concomitant products included LEVOTHYROXINE for an unknown indication.   On 16-Jun-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 14-Jul-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 15-Jul-2021, the patient experienced ARRHYTHMIA (Arrhythmia/ her heart rate went up and down) (seriousness criterion medically significant). On an unknown date, the patient experienced DISCOMFORT (feels something very heavy on her). The patient was treated with APIXABAN (ELIQUIS) for Anticoagulant therapy, at an unspecified dose and frequency. At the time of the report, ARRHYTHMIA (Arrhythmia/ her heart rate went up and down) had not resolved and DISCOMFORT (feels something very heavy on her) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 15-Jul-2021, Heart rate: heart rate went up and down on The next day following vaccination with the second dose patient's heart rate went up and down on certain days, not every day, and she experienced arrhythmias.         Patient stated she experienced pretty nasty side effects from the vaccine. Patient mentioned that she though within 4 months it should go away but she was still dealing with this symptoms. Patient told that there were no history in her family for this she never had any issues on that.  The patient has not diagnosed with COVID 19 or tested for COVID. The patient had no medical history relating to mentioned adverse events Acute and Chronic illnesses at the time of vaccination. Recent change in status such as improvement or worsening sometimes she has really good days. And the heart rate goes up and it is very hard to lower it down.  No other vaccines were given within 1 month prior to Moderna COVID-19 vaccine. patient to seek medical care as patient was not hospitalized, but yes she had to look for medical care.  The patient has not experienced a similar event in the past.  She goes day by day, she has a monitor in her watch, when the heart rate was high she rests.  Company Comment: This spontaneous case concerns a 68-year-old female patient with relevant medical history of Graves' disease with post thyroidectomy state and concomitantly taking levothyroxine, who experienced the unexpected, serious (medically significant) adverse event of special interest of arrhythmia, that occurred after receiving second dose of mRNA-1273 vaccine. She reported that the next day following vaccination with the second dose, her heart rate went up and down on certain days and she experienced arrhythmias. Patient took medical care for the treatment of event; however, further details on clinical course, diagnostic tests performed, and treatment specifics were not provided. Outcome of the event arrhythmia was reported as not recovered. Hypothyroid state with concomitant use levothyroxine remains as strong confounder for the event of arrhythmia. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.   This case was linked to MOD-2022-537766.; Sender's Comments: This spontaneous case concerns a 68-year-old female patient with relevant medical history of Graves' disease with post thyroidectomy state and concomitantly taking levothyroxine, who experienced the unexpected, serious (medically significant) adverse event of special interest of arrhythmia, that occurred after receiving second dose of mRNA-1273 vaccine. She reported that the next day following vaccination with the second dose, her heart rate went up and down on certain days and she experienced arrhythmias. Patient took medical care for the treatment of event; however, further details on clinical course, diagnostic tests performed, and treatment specifics were not provided. Outcome of the event arrhythmia was reported as not recovered. Hypothyroid state with concomitant use levothyroxine remains as strong confounder for the event of arrhythmia. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.