I had a four hour bout of supraventricular tachycardia a few hours after my Moderna (full-dose) booster (3rd vaccine), then 10 days later went into a six week period of frequent A-fib bouts that finally landed me in the ER. I'm on Elliquis and a very low dose of Metoprolol now, and have not had any more incidences. My cardiac history includes an exercise stress test three years ago as a result of my detecting some heart palpitations. That was normal. Three months prior to the booster, after a sleepless, stressful night with quite a few shots of whiskey, I had a horrible a bout of very disturbing palpitations, which in retrospect I think was A-fib. I feel like I had some predilection towards A-fib prirot to the booster. However I can't help but think the vaccine somehow impacted my heart and the ensuing several months of arrythmias.