rapid irregular heart beats after 3rd dose; a lot of headache like her head was boiling; she also experienced a fever of 103 degree Fahrenheit; This spontaneous case was reported by a consumer and describes the occurrence of ARRHYTHMIA (rapid irregular heart beats after 3rd dose) in a 55-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 052E21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Penicillin allergy, Latex allergy, Heart disorder, Multiple sclerosis (There was no recent change in status such as improvement or worsening) since 1995, Stomach function disorder and Arrhythmia (The patient experienced rapid irregular heart beats even before getting any of the vaccines, because she had heart problems). Concomitant products included ACEBUTOLOL for Arrhythmia, PANTOPRAZOLE for Stomach function disorder, OCRELIZUMAB (OCREVUS), GABAPENTIN, ROPINIROLE, BACLOFEN, BUPROPION HYDROCHLORIDE (WELLBUTRIN), DIAZEPAM, HYDROCHLOROTHIAZIDE, TRIAMTERENE (TRIAMTERENE/HCTZ), DICYCLOMINE [DICYCLOVERINE], PROMETHAZINE and MELOXICAM (MOBIC) for an unknown indication.    On 29-Aug-2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 29-Aug-2021, the patient experienced HEADACHE (a lot of headache like her head was boiling) and PYREXIA (she also experienced a fever of 103 degree Fahrenheit). On an unknown date, the patient experienced ARRHYTHMIA (rapid irregular heart beats after 3rd dose) (seriousness criterion medically significant). The patient was treated with PARACETAMOL (TYLENOL [PARACETAMOL]) for Fever, at an unspecified dose and frequency and IBUPROFEN for Fever, at an unspecified dose and frequency. On 31-Aug-2021, HEADACHE (a lot of headache like her head was boiling) and PYREXIA (she also experienced a fever of 103 degree Fahrenheit) had resolved. At the time of the report, ARRHYTHMIA (rapid irregular heart beats after 3rd dose) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 29-Aug-2021, Body temperature: 103 (High) 103 degree Fahrenheit. On an unknown date, Heart rate: rapid irregular heart beats (abnormal) rapid irregular heart beats.         The patient did not have a history of Myocarditis/pericarditis. The patient never had COVID positive test or diagnosis. The patient did not receive any other vaccines within 1 month prior to Moderna COVID-19 vaccine. Due to the headache, the patient needed to put an ice pack on her head. Despite taking the treatment for fever, it did not go down with anything after 3 days.  The adverse events did not cause the patient to seek medical care (office visit, urgent care, ER, hospitalized).  Company comment: This spontaneous case concerns a 55 year old female with relevant medical history of  multiple sclerosis ( stable condition )  , heart disorder and cardiac arrhythmia , who experienced serious ( medically significant ) , unexpected , AESI event of arrhythmia  which occurred on an unknown date post vaccination with the  3rd dose of mRNA-1273 vaccine. On the same day post vaccination with the 3rd dose of mRNA-1273 vaccine this patient experienced non-serious , expected events of headache and pyrexia . This patient was treated with paracetamol and ibuprofen and ice pack . The patient did not  seek  any medical care (office visit, urgent care, ER, hospitalized) and also no laboratories /diagnostic procedures were reported . This patient  had  low grade fever after the first two doses of mRNA-1273 vaccine which resolved spontaneously however for the third dose it was continuous and needed medication and resolved after 3 days. So for the event of pyrexia it is positive re-challenge. Event of arrhythmia , headache and fever was also reported for the 4th dose of the mRNA-1273 vaccine hence possible positive re-challenge for the event headache and fever. The outcome of the event arrhythmia for the dose 3 is unknown and for the events headache and fever it is resolved. The above medical history of Cardiac arrhythmia  , cardiac disorder and multiple sclerosis are considered as confounders for the event arrhythmia while for the event of fever and headache her medical condition of multiple sclerosis is a confounder. The benefit -risk relationship of mRNA -1273 ( Moderna Covid 19 Vaccine) is not affected by this report   This case was linked to MOD-2022-517635, MOD-2022-517697 (Patient Link).; Sender's Comments: This spontaneous case concerns a 55 year old female with relevant medical history of  multiple sclerosis ( stable condition )  , heart disorder and cardiac arrhythmia , who experienced serious ( medically significant ) , unexpected , AESI event of arrhythmia  which occurred on an unknown date post vaccination with the  3rd dose of mRNA-1273 vaccine. On the same day post vaccination with the 3rd dose of mRNA-1273 vaccine this patient experienced non-serious , expected events of headache and pyrexia . This patient was treated with paracetamol and ibuprofen and ice pack . The patient did not  seek  any medical care (office visit, urgent care, ER, hospitalized) and also no laboratories /diagnostic procedures were reported . This patient  had  low grade fever after the first two doses of mRNA-1273 vaccine which resolved spontaneously however for the third dose it was continuous and needed medication and resolved after 3 days. So for the event of pyrexia it is positive re-challenge. Event of arrhythmia , headache and fever was also reported for the 4th dose of the mRNA-1273 vaccine hence possible positive re-challenge for the event headache and fever. The outcome of the event arrhythmia for the dose 3 is unknown and for the events headache and fever it is resolved. The above medical history of Cardiac arrhythmia  , cardiac disorder and multiple sclerosis are considered as confounders for the event arrhythmia while for the event of fever and headache her medical condition of multiple sclerosis is a confounder. The benefit -risk relationship of mRNA -1273 ( Moderna Covid 19 Vaccine) is not affected by this report