and decompensation cordis; atrial fibrillation; day after vaccination, tightness complaints; this case was received via the regulatory authority (reference number: nl-lrb-00780829) on 17-feb-2022 and was forwarded to moderna on 17-feb-2022. this regulatory authority case was reported by a physician and describes the occurrence of cardiac failure (and decompensation cordis), atrial fibrillation (atrial fibrillation) and dyspnoea (day after vaccination, tightness complaints) in a 46-year-old male patient who received mrna-1273 (spikevax) (batch no. 216041bs) for covid-19 vaccination. previously administered products included for product used for unknown indication: biontech/pfizer vaccin (comirnaty) covid-19 vaccin pfizer injvlst 0,3ml on 09-jun-2021, biontech/pfizer vaccin (comirnaty) covid-19 vaccin pfizer injvlst 0 and3ml on 14-jul-2021. past adverse reactions to the above products included no adverse event with biontech/pfizer vaccin (comirnaty) covid-19 vaccin pfizer injvlst 0,3ml, biontech/pfizer vaccin (comirnaty) covid-19 vaccin pfizer injvlst 0 and3ml. on 02-jan-2022, the patient received dose of mrna-1273 (spikevax) (unknown route) 1 dosage form. on 03-jan-2022, the patient experienced cardiac failure (and decompensation cordis) (seriousness criterion hospitalization), atrial fibrillation (atrial fibrillation) (seriousness criterion hospitalization) and dyspnoea (day after vaccination, tightness complaints) (seriousness criterion hospitalization). at the time of the report, cardiac failure (and decompensation cordis), atrial fibrillation (atrial fibrillation) and dyspnoea (day after vaccination, tightness complaints) outcome was unknown. for mrna-1273 (spikevax) (unknown), the reporter did not provide any causality assessments. concomitant medication was not reported. treatment medication was not reported. company comment: this regulatory case concerns a 46-year-old male patient, with history of interchange of vaccine products (two doses of biontech/pfizer vaccine), experienced the unexpected serious adr events cardiac failure, atrial fibrillation, and unexpected serious event dyspnoea, one day after a dose of mrna-1273. the patient was hospitalized for the events. at the time of reporting, the outcome of the events was unknown. the benefit-risk relationship of mrna-1273 is not affected by this report. event seriousness assessed as per regulatory authority reporting.; sender's comments: this regulatory case concerns a 46-year-old male patient, with history of interchange of vaccine products (two doses of biontech/pfizer vaccine), experienced the unexpected serious adr events cardiac failure, atrial fibrillation, and unexpected serious event dyspnoea, one day after a dose of mrna-1273. the patient was hospitalized for the events. at the time of reporting, the outcome of the events was unknown. the benefit-risk relationship of mrna-1273 is not affected by this report. event seriousness assessed as per regulatory authority reporting