Hello, @chickenfarmer My cardiologists, and the literature, have admitted for many years now that low thyroid (hypothyroidism) also causes heart arrhythmias, although it's not clearly understood why and how this occurs. Previously, it was believed that only high thyroid triggered atrial fib, and that was taught in med school for years. But it's a complex relationship between heart & thyroid. "Stop The Thyroid Madness" is a patient-centered website (and a book by that name) that has been compiling research on this and other thyroid questions and treatments for almost 25 years, and might be of interest to you. There are research studies discussed and other documentation of doctors who are studying the low-thyroid/afib connection. I found it helpful; I have low thyroid and AF episodes.