a-fib; Heart shocked into rhythm; a-fib/shocked heart beat into rhythm; Low oxygen - very short of breath; This is a spontaneous report received from a contactable reporter(s) (Consumer or other non HCP) for a Pfizer sponsored program (159558). The reporter is the patient.  A 83 year-old female patient received bnt162b2 (BNT162B2), intramuscular, administered in arm left, administration date 20Feb2021 11:00 (Lot number: EM9809) at the age of 83 years as dose 2, single and intramuscular, administered in arm left, administration date 17Sep2021 (Lot number: EW0162) as dose 3 (booster), single for covid-19 immunization. Relevant medical history included: "Multiple Sclerosis", start date: 2005 (ongoing); "Pulmonary Hypertension" (ongoing), notes: Heart Catheter 2014 and 2019; "Osteoporosis" (ongoing), notes: Rt knee replaced 2011, left hip replaced 2018; "Loss of vision in upper quadrant of left eye" (ongoing); "Interstitial lung disease", start date: 2014 (ongoing), notes: 03Jun2021 had pneumonia chest x-ray.; "Atrial Fibrillation" (ongoing). Family history included: "Osteoporosis" (unspecified if ongoing), notes: Mother; "Congestive Heart Failure" (unspecified if ongoing), notes: Father. There were no concomitant medications. Vaccination history included: Bnt162b2 (Dose: 1, Date: 30Jan2021, Time: 11:00 am, Anatomical Site of injection: Left Arm, Route of administration: Intramuscular, Batch/Lot Number: Pfizer EL3247), administration date: 30Jan2021, for COVID-19 immunization. The following information was reported: ATRIAL FIBRILLATION (medically significant) with onset 09Jun2021, outcome "unknown", described as "a-fib/shocked heart beat into rhythm"; DYSPNOEA (medically significant) with onset 09Jun2021, outcome "unknown", described as "Low oxygen - very short of breath"; ATRIAL FIBRILLATION (hospitalization, medically significant) with onset 07Jul2021, outcome "recovered with sequelae" (2021), described as "a-fib"; ARRHYTHMIA (hospitalization) with onset 30Jun2021, outcome "recovering", described as "Heart shocked into rhythm". The patient was hospitalized for atrial fibrillation (hospitalization duration: 5 day(s)); for arrhythmia (hospitalization duration: 4 day(s)). The events "a-fib" and "heart shocked into rhythm" were evaluated at the emergency room visit. The patient underwent the following laboratory tests and procedures: blood test: (02Aug2021) bnb385; chest x-ray: (01Mar2017) chronic fibrotic multinodular thyroid gland change, notes: Chronic Fibrotic Multinodular thyroid gland changes of lungs, Observed - Thyroid scan every year; (03Jun2021) pneumonia, notes: Antibiotics given; covid-19: (02Aug2021) negative, notes: HCF; magnetic resonance imaging: (09Dec2014) t-12 fracture vertebral, notes: Wore Brace; (10Nov2015) some changes; (26Mar2020) not much change; magnetic resonance imaging head: (26Mar2020) not much change; oxygen saturation decreased: (09Jun2021) unknown results, notes: Low oxygen - very short of breath. Therapeutic measures were taken as a result of atrial fibrillation, arrhythmia. Clinical course was reported as the patient did not received any prior vaccinations with 4 weeks of vaccination. A-Fib Stop date was reported as ongoing. Pertinent Details included Abiated and filled flutter (07Jul2021). Onset time for shocked heart beat into rhythm was reported as evening of 30Jun2021. Patient received 2 new medication for A-Fib. Treatment received for shocked heart beat into rhythm was Ablation. It was reported that there was no autopsy information presented at the time of the report.  Follow up (28Dec2021): This is a follow-up spontaneous report received from a contactable consumer. This consumer (patient) reported in response to Non-HCP letter sent which included that, the case is now valid with all the information.  Follow-up attempts are not possible. No further information is expected.