I don't need a study to learn that Pfizer/biontech vaccines mess up with heart rate, especially when excercising. I know that from personal experience. The heart rate issues seem to be long lasting, but the vaccines are no good after 6 months, as we know now. My problem is that if just 2 shots cause such effect, then after a few boosters I'll have to take heart rate control pills. I'd rather pass on boosters and use the good old masks and social distancing.