Elevated heart rate/ heart rate was erratic; Arm was sore; Itches for a few hours; This is a spontaneous report received from a contactable reporter(s) (Consumer or other non HCP) from medical information team. The reporter is the patient.  A 80 year-old female patient received bnt162b2 (COMIRNATY), administration date 20Oct2021 09:30 (Batch/Lot number: unknown) as dose 3 (booster), single for covid-19 immunisation. The patient's relevant medical history and concomitant medications were not reported. Vaccination history included: Bnt162b2 (Dose: 1), for COVID-19 Immunization; Bnt162b2 (Dose: 2), for COVID-19 Immunization, reaction(s): "Itches at the injection site", "Low grade fever"; Yellow fever, for immunization; Encephalitis, for immunization; Seasonal flu vaccine (on the opposite arm), for immunization.  The following information was reported: HEART RATE INCREASED (medically significant) with onset 21Oct2021, outcome "recovered" (21Oct2021), described as "Elevated heart rate/ heart rate was erratic"; PAIN IN EXTREMITY (non-serious) with onset 21Oct2021, outcome "recovered" (21Oct2021), described as "Arm was sore"; PRURITUS (non-serious) with onset 21Oct2021, outcome "recovered" (21Oct2021), described as "Itches for a few hours". The patient underwent the following laboratory tests and procedures: heart rate: (21Oct2021) elevated; (21Oct2021) 82; (21Oct2021) 79; (21Oct2021) 66; (21Oct2021) 78-115; (21Oct2021) 115, notes: erratic.  Clinical course: The patient got the booster dose of the Pfizer BioNtech Covid-19 Vaccine yesterday at around 9:30 in the morning (time zone was not specified) and when she woke up this morning, her pulse oximeter's app reading was at 66. The patient also stated that her heart rate was erratic, one reading was at 78-115. Caller stated that she noticed it at around 10:30 in the morning pacific daylight time today. She stated that normally it was at 61 to 62 and also provided background information that back then around 2009, she is very active and did some hiking. She also stated that she walks 3 miles every other day. She also stated that when she woke up this morning, her noticed that her arm was sore and itches for a few hours. She also stated that she also got a seasonal flu vaccine on the opposite arm. She stated she feels okay and didn't notice edema but what concerned her was the elevated heart rate. She  read her pulse oximeter while on the call and stated it was at 82 and the second reading was at 79. Normally after first one she didn't feel anything and then after the second dose she normally felt itches at the injection site and had a low grade fever after 24 hours that lasted for 5 hours. She is concerned since when she woke up her arm was sore and that is fine, no big deal. She noticed since she has a smart watch and it monitors her sleep habits and she noticed that her resting heart rate was higher. Her normal resting heart rate is around 61 or 62. Her resting heart rate was up to 66 this morning. She went out and worked in her yard for two hours and her heart rate now is very erratic and has been up to 115, she monitors it on different devices like heart app, and pulse ox monitor. Asking if should she be concerned that her heart rate is so erratic running from 78 to 115. Should she consider going to the ER. She feels fine.  The lot/batch number is not available despite the follow-up attempts made. Follow-up attempts completed. No further information is expected.