myocardial event, with smoldering heart failure which resolved almost completely 6 months later, but EF went from 65% to 40%; brain fog; tinnitus; a covid infection; fatigue; rashes; muscle aches; This spontaneous case was reported by a patient and describes the occurrence of CARDIAC FAILURE (myocardial event, with smoldering heart failure which resolved almost completely 6 months later, but EF went from 65% to 40%) in a 50-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.    On an unknown date, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On an unknown date, the patient experienced CARDIAC FAILURE (myocardial event, with smoldering heart failure which resolved almost completely 6 months later, but EF went from 65% to 40%) (seriousness criterion medically significant), FEELING ABNORMAL (brain fog), TINNITUS (tinnitus), COVID-19 (a covid infection), FATIGUE (fatigue), RASH (rashes) and MYALGIA (muscle aches). At the time of the report, CARDIAC FAILURE (myocardial event, with smoldering heart failure which resolved almost completely 6 months later, but EF went from 65% to 40%), TINNITUS (tinnitus), COVID-19 (a covid infection), FATIGUE (fatigue), RASH (rashes) and MYALGIA (muscle aches) had not resolved and FEELING ABNORMAL (brain fog) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Ejection fraction: EF went from 65% to 40%.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter did not provide any causality assessments.   No concomitant product reported by the reporter.  Patient had myocardial event, with smoldering heart failure which resolved almost completely 6 months later, but EF went from 65% to 40% and patient was very sick. Patient continued to suffer from episode fatigue, rashes, muscle aches, tinnitus, and brain fog, these things flare after a COVID infection as well. It was unknown if the patient experienced any additional symptoms or events.  No treatment medication reported by reporter.  Company comment.  This spontaneous case reported by the patient concerns a 50  year  old female patient, with no medical history reported, who experienced the unexpected, serious (medically significant) AESI of cardiac failure on an unknown date after receiving the 2 dose of mRNA  1273 original vaccine in the covid 19 vaccine series. Reportedly, the patient experienced a smoldering heart failure which resolved almost completely 6 months later; her ejection fraction went from 65% to 40%. She mentioned she continued suffering episodes of fatigue, rashes, muscle aches, tinnitus, and brain fog, and that "these things flared after a COVID infection as well". The outcome of the event was not recovered. No further information on patient´s previous immunization schedule, concomitant medications and treatment details  were provided for medical reviewing. The benefit-risk relationship of mRNA  1273 original vaccine is not affected by this report.