HELP, PLEASE! My mother was given 3x the dosage of synthroid and unknowingly took it for about 1 month. She went into A-Fib due to this occurrence. She continued in and out of A-fib until she was finally referred by a friend to another heart doctor that performed an ablasion on her heart. She still has episodes of it going into A-fib occassionally but it corrects itself.  She had no previous problem like this till the overdose was given even though she had rheumatic fever as a child and has two leakages in her heart. Is it your professional opinion that she would have had this happen eventually because of her childhood illness or was it brought on by the synthroid OD?