Congestive heart failure (Stage 2); occasional angina during acitivty; more fatigue; irregular heartbeat after cardioversion; Atrial fibrillation and 2 ER visits, 2 days in a row; This case was received via an unknown source (no reference has been entered for a health authority or license partner) on 28-Mar-2021 and was forwarded to Moderna on 29-Mar-2021.    This spontaneous case was reported by a nurse (subsequently medically confirmed) and describes the occurrence of CARDIAC FAILURE CONGESTIVE (Congestive heart failure (Stage 2)), ATRIAL FIBRILLATION (Atrial fibrillation and 2 ER visits, 2 days in a row) and ANGINA PECTORIS (occasional angina during acitivty) in a 77-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 025L20A and 042L20A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Mercury sensitivity (itching, tearing; reacted once), Shellfish allergy (rash) and Hypertrophic cardiomyopathy. Concomitant products included AMIODARONE from 06-Feb-2021 to an unknown date for Atrial fibrillation, METOPROLOL SUCCINATE (TOPROL XL) and RIVAROXABAN (XARELTO) for an unknown indication.   On 05-Jan-2021 at 1:00 PM, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 02-Feb-2021 at 4:00 PM, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On 05-Feb-2021, the patient experienced ATRIAL FIBRILLATION (Atrial fibrillation and 2 ER visits, 2 days in a row) (seriousness criterion medically significant). On 06-Feb-2021, the patient experienced HEART RATE IRREGULAR (irregular heartbeat after cardioversion). On 14-Feb-2021, the patient experienced CARDIAC FAILURE CONGESTIVE (Congestive heart failure (Stage 2)) (seriousness criteria hospitalization and medically significant). On an unknown date, the patient experienced ANGINA PECTORIS (occasional angina during acitivty) (seriousness criterion medically significant) and FATIGUE (more fatigue). The patient was hospitalized from 14-Feb-2021 to 16-Feb-2021 due to CARDIAC FAILURE CONGESTIVE. At the time of the report, CARDIAC FAILURE CONGESTIVE (Congestive heart failure (Stage 2)) and ATRIAL FIBRILLATION (Atrial fibrillation and 2 ER visits, 2 days in a row) had resolved and ANGINA PECTORIS (occasional angina during acitivty), HEART RATE IRREGULAR (irregular heartbeat after cardioversion) and FATIGUE (more fatigue) had not resolved.        For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter considered ATRIAL FIBRILLATION (Atrial fibrillation and 2 ER visits, 2 days in a row) to be possibly related. No further causality assessments were provided for CARDIAC FAILURE CONGESTIVE (Congestive heart failure (Stage 2)), ANGINA PECTORIS (occasional angina during acitivty), HEART RATE IRREGULAR (irregular heartbeat after cardioversion) and FATIGUE (more fatigue).    The patient was treated with cardioversion on 06-FEB-2021 and IV Lasix.  Very limited information regarding these events has been provided at this time. The CHF was attributed to the use of the amiodarone for aggravated atrial fibrillation. No further follow-up information is expected.   This case was linked to MOD-2021-006529 (E2B Linked Report). This case was linked to MOD-2021-006529 (Patient Link).; Sender's Comments: Very limited information regarding these events has been provided at this time. The CHF was attributed to the use of the amiodarone for aggravated atrial fibrillation. No further follow-up information is expected. MOD-2021-006529:Same patient, 1st dose