Inappropriate schedule of vaccine administered; Increased arrhythmia; palpitations; chest pain/pain on the left side of the chest that did not radiate; increased shortness of breath; Lip tingling; intermittent pain; Condition aggravated; This spontaneous case was reported by a pharmacist and describes the occurrence of ARRHYTHMIA (Increased arrhythmia) in a 45-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 042L20A and 025J20-2A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Wolff-Parkinson-White syndrome congenital, Cardiac arrhythmia (due to a condition they were born with called Wolff Parkinson White) and Tachycardia. Concomitant products included ATENOLOL for Tachycardia, ALBUTEROL [SALBUTAMOL], BECLOMETASONE DIPROPIONATE (QVAR) and VITAMINS NOS for an unknown indication.   On 23-Dec-2020, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 28-Jan-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 02-Feb-2021, the patient experienced ARRHYTHMIA (Increased arrhythmia) (seriousness criterion medically significant), PALPITATIONS (palpitations), CHEST PAIN (chest pain/pain on the left side of the chest that did not radiate), DYSPNOEA (increased shortness of breath), PARAESTHESIA ORAL (Lip tingling), PAIN (intermittent pain) and CONDITION AGGRAVATED (Condition aggravated). On an unknown date, the patient experienced INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION (Inappropriate schedule of vaccine administered). The patient was treated with FLECAINIDE for Adverse event, at an unspecified dose and frequency. At the time of the report, ARRHYTHMIA (Increased arrhythmia), PALPITATIONS (palpitations), CHEST PAIN (chest pain/pain on the left side of the chest that did not radiate), DYSPNOEA (increased shortness of breath), PARAESTHESIA ORAL (Lip tingling), PAIN (intermittent pain), CONDITION AGGRAVATED (Condition aggravated) and INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION (Inappropriate schedule of vaccine administered) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 02-Feb-2021, Electrocardiogram: normal (normal) normal.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   As per the reporter, the normal results might be because they had to wait for the machine for a while and were in the supine position for a period of time before getting it done. Patient wore a holter monitor for 48 hours as part of the treatment.  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. Concomitant medical condition Wolf Parkinson White could be a potentially confounder for the events.; 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. Concomitant medical condition Wolf Parkinson White could be a potentially confounder for the events.