diastolic heart failure; went into AFib; went into AFib/ Had not had AFib episodes or been to hospital for AFib since 2017; This is a spontaneous report received from a contactable reporter(s) (Other HCP). The reporter is the patient.  A 55 year-old female patient (not pregnant) received bnt162b2 (PFIZER-BIONTECH COVID-19 mRNA VACCINE), administered in arm right, administration date 27Jan2021 17:00 (Lot number: EJ1686) at the age of 55 years as dose 2, single for covid-19 immunisation. Relevant medical history included: "Penicillin" (unspecified if ongoing), notes: allergies; "Bees stings" (unspecified if ongoing), notes: allergies; "AFib" (until 2017); "sleep apnea" (unspecified if ongoing); "svt" (unspecified if ongoing); "obesity" (unspecified if ongoing); "asthma" (ongoing). Patient did not receive other vaccines within 4 weeks of the COVID-19 vaccine. Patient did not have COVID prior to vaccination. Concomitant medication(s) included: DILTIAZEM; FLECAINIDE; XARELTO; LASIX [FUROSEMIDE SODIUM]; POTASSIUM; TRIAZ [AZITHROMYCIN]. Past drug history included: Morphine, reaction(s): "allergies:morphine"; Keflex, reaction(s): "allergies:Keflex"; Levaquin, reaction(s): "allergies: levaquin"; Xanax, reaction(s): "allergies: Xanax"; Aspartame, reaction(s): "allergies:aspartame"; Metprolol, reaction(s): "allergies: metprolol"; Erythromycin, reaction(s): "allergies: erythromycin"; Breo, reaction(s): "known allergies: breo"; Versed, reaction(s): "known allergies: versed". Vaccination history included: Bnt162b2 (Dose 1, lot number=EL9261, administration time=05:00PM, location Right arm), administration date: 05Jan2021, when the patient was 55 years old, for COVID-19 immunization, reaction(s): "out of AFib". The following information was reported: ATRIAL FIBRILLATION (hospitalization) with onset 30Jan2021, outcome "unknown", described as "went into AFib"; DISEASE RECURRENCE (hospitalization) with onset 30Jan2021, outcome "unknown", described as "went into AFib/ Had not had AFib episodes or been to hospital for AFib since 2017"; LEFT VENTRICULAR FAILURE (hospitalization) with onset Mar2021, outcome "unknown", described as "diastolic heart failure". The patient was hospitalized for atrial fibrillation and disease recurrence (start date: 30Jan2021, hospitalization duration: 1 day(s)); for left ventricular failure (hospitalization duration: 1 day(s)). The events "went into afib", "went into AFib/ Had not had AFib episodes or been to hospital for AFib since 2017" and "diastolic heart failure" were evaluated at the physician office visit and emergency room visit. The patient underwent the following laboratory tests and procedures: sars-cov-2 test: (30Jan2021) negative, notes: Nasal Swab. Therapeutic measures were taken as a result of atrial fibrillation, disease recurrence, left ventricular failure which included diltiazem (CARDIZEM) drip.  Clinical course was described as follows: After the 2nd vaccine, patient went into AFib on Saturday (30Jan2021) went to hospital, 10Mar2021 went into AFib went to hospital, end of Mar2021 and middle of Apr2021 AFib again stayed home and eventually stopped. Patient stated she had not had AFib episodes or been to hospital for AFib since 2017. In Mar2021 showed some diastolic heart failure during that admission. Patient stated she has had issues all year.; Sender's Comments: Based on the temporal relationship the reasonable possibility of an association between the reported events and suspect product bnt162b2 cannot be ruled out.The underlying medical conditions could offer an alternate explanation for the reported events, The impact of this report on the benefit/risk profile of the Pfizer product is evaluated as part of Pfizer procedures for safety evaluation, including the review and analysis of aggregate data for adverse events. Any safety concern identified as part of this review, as well as any appropriate action in response, will be promptly notified to RAs, Ethics Committees, and Investigators, as appropriate.,Linked Report(s) : -PFIZER INC-202101655168 Same reporter/SD, Different potential/AE