I had my second dose of the Pfizer vaccine in early February, 2021 and 6 weeks later, through a routine medical exam, learned that my resting heart rate had jumped to 120 bpm and was arrhythmic. I'd had no prior history of arrhythmia and none in family, but I had been diagnosed several years earlier with Sinus Bradycardia. Since March, when the arrhythmia/tachycardia was found, Ive had two ablations, the most recent in September. I am experiencing post-ablation symptoms of tachycardia and arrhythmia which have so far resolved. In the course of treating my atrial flutter, I spoke to two separate nurses on two separate occasions who asked me (perhaps out of general interest) if my arrhythmia had started after receiving the vaccine. When I told them it had and asked if they knew of a connection, both replied, "They just don't know". This has not been reassuring in helping me to move forward with the booster shot! I am sure that my cardiologist and GP will tell me that the risks of Covid 19 are far greater than the risks of arrhythmia from the vaccine and I think they would be right, but I wish I felt more sanguine about it. My sister at age 63 had one of the rare side effects of pericarditis from her second dose of the Pfizer vaccine, but it resolved within a few days.