I was having heart problems I had to be hospitalized and observed for 24 hours/I had a really fast heart rate it reached 155bpm; fluttering; I had shortness of breath; heart palpitations; After the vaccine I had nausea; After the vaccine I had headache; After the vaccine I had body ache; Arm pain; Patient received second dose more than 35 days after the first dose of the Moderna COVID-19 vaccine; This spontaneous case was reported by a consumer and describes the occurrence of HEART RATE INCREASED (I was having heart problems I had to be hospitalized and observed for 24 hours/I had a really fast heart rate it reached 155bpm) and CARDIAC FLUTTER (fluttering) in a 62-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 0MB21A and 022M20A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.  Concomitant products included THYROID (ARMOUR THYROID), CIMETIDINE, SULFAMETHOXAZOLE, TRIMETHOPRIM (BACTRIM), OXYBUTYNIN, PHENTERMINE, TOPIRAMATE, HYDROXYZINE, PREDNISONE, SPIRONOLACTONE, ESZOPICLONE (LUNESTA), LEVOCETIRIZINE DIHYDROCHLORIDE (XYZAL), FEXOFENADINE HYDROCHLORIDE (ALLEGRA), FLUTICASONE and METHENAMINE for an unknown indication.   On 28-Feb-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 13-Apr-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 13-Apr-2021, the patient experienced INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION (Patient received second dose more than 35 days after the first dose of the Moderna COVID-19 vaccine). On 14-Apr-2021, the patient experienced PAIN (After the vaccine I had body ache), PAIN IN EXTREMITY (Arm pain), NAUSEA (After the vaccine I had nausea) and HEADACHE (After the vaccine I had headache). On 29-Aug-2021, the patient experienced HEART RATE INCREASED (I was having heart problems I had to be hospitalized and observed for 24 hours/I had a really fast heart rate it reached 155bpm) (seriousness criterion hospitalization), CARDIAC FLUTTER (fluttering) (seriousness criterion medically significant), DYSPNOEA (I had shortness of breath) and PALPITATIONS (heart palpitations). The patient was hospitalized for 1 day due to HEART RATE INCREASED. At the time of the report, HEART RATE INCREASED (I was having heart problems I had to be hospitalized and observed for 24 hours/I had a really fast heart rate it reached 155bpm), CARDIAC FLUTTER (fluttering), DYSPNOEA (I had shortness of breath) and PALPITATIONS (heart palpitations) outcome was unknown and PAIN (After the vaccine I had body ache), PAIN IN EXTREMITY (Arm pain), NAUSEA (After the vaccine I had nausea), HEADACHE (After the vaccine I had headache) and INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION (Patient received second dose more than 35 days after the first dose of the Moderna COVID-19 vaccine) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 29-Aug-2021, Heart rate: 155 (High) rapid heart rate of 155 beats per minute and was hospitalized for 24 hours.         Treatment medication was not provided by the reporter.  The patient reports that on 29 Aug 2021 she had an episode where she experienced rapid heart rate of 155 beats per minute and was hospitalized for 24 hours.  Company comment: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded.   This case was linked to MOD-2021-309020.; Sender's Comments: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded.