Shortly after receiving my Moderna booster I was at the gym doing Cardio exercise. My heart rate was close to 200 bpm. I thought the machine I was on was malfunctioning and switched, same result. I went home and using my Kardia found that I was in a fib. I am in good shape and never before had this issue. I found a cardiologist, had a TEE and have not had any issues since. I am convinced the vaccine caused my a fib.