True it is known, there is a connection btw. a state of hyperthyroid, and heart palpitations, arhythmia and tachycardia, link below. So, it is possible that long-term taking high amounts of Iodine could be problematic. We just don't know, or, at least, I have not seen any study where any subjects were given high amounts of Iodine for extended period. I personally took large amounts, several years ago, for the purpose of eliminating metals, but I quit doing that after a couple months.