This is a spontaneous report received from a contactable reporter (Consumer) from medical information team for a Pfizer sponsored program. The reporter is the patient. A 55-year-old female patient received bnt162b2 (BNT162B2), administered in arm left, administration date 19Apr2021 16:15 (Lot number: ER8731, Expiration Date: Jul2021) at the age of 55 years as dose 2, single for Covid-19 immunisation. Relevant medical history included: "doesn't have a spleen" (unspecified if ongoing). The patient's concomitant medications were not reported. Vaccination history included: Bnt162b2 (DOSE 1, Arm Left, Lot number: EP6955, Expiration date: Jun2021), administration date: 27Mar2021, when the patient was 55 years old, for COVID-19 immunisation. The following information was reported: ATRIAL FIBRILLATION (medically significant) with onset Aug2021, outcome "unknown", described as "AFib (atrial fibrillation)". The event "AFib (atrial fibrillation)" was evaluated at the physician office visit. She said she experienced increase in heart rate every time she has icy cold drinks, then it also happens whenever she tries to lie down. These events happened around August, in total of 4 events, she has seen a doctor and was referred to a cardiologist; she was recommended to have a heart monitor for tracking. Patient said the diagnosis made by healthcare professional was AFib (atrial fibrillation), and she wanted to know if this is linked to the vaccine. She thinks it's the vaccine for corona virus, but she wasn't sure. She had the Pfizer, and she had some weird things going on since then. She said one doctor said no. She states it boils down to AFib and in the very beginning when she would drink icy cold drinks her heartrate would go sky high. Went to primary and cardiologist and did heart monitors and Doctor told her to try to recreate. She was able to successfully recreate it and they called it AFib. Doctor didn't think it was related to the icy cold drinks. She had another monitor that didn't match and couldn't recreate, because stopped drinking icy cold drinks. She was put on medication and when medication didn't work, they doubled the medication. States it's just so coincidental even though they say it can't be from the vaccine. Did not have diagnosis for AFib at the time in Apr2021. She states up until that point she had only four things with the icy cold drinks up until this 22Nov2021 and it's been downhill since then. From Apr thru Aug, she has had four events she thinks. The patient underwent the following laboratory tests and procedures: c-reactive protein (HRCRP): (Dec2021) 7.0, notes: inflammation marked for that was 7.0; echocardiogram: (Dec2021) they didn't find anything; Holter monitoring: (20Oct2021) unknown result; (Dec2021) unknown result. Doctor who recommends vaccine is now retired. Her booster date was on 22Nov2021 at 4:30. She started to see this naturopathic doctor and he did blood work and that everything was good during the same time frame but just after probably 1st and 2nd dose, on her first visit. Therapeutic measures were taken as a result of atrial fibrillation. Medication started for AFib: metoprolol 25 mg started daily tablet by mouth. Medication has given her 3 days of relief but that's it, not in a row. Follow-up attempts are completed. No further information is expected.