I'm wondering if anyone else has been told this. Went to drs this pm to ask about a rash and possible adverse drug reaction.......I've been prescribed warfarin and beta blocker for a dx of AF since november.....it only happened once. Anyway as my TSH was just over range and T4 13.2 I asked if I could have a trial dose of 25mg thyroxine. The doc told me that 25mg would / could cause me to have another attack of AF and they would not prescribe thyroxine until TSH was 10. I have a resting heart rate of 48 to 55 with an average BP of 116/58. Has anyone else had similar or throw some light on this?