Endogenous subclinical hyperthyroidism appears to be associated with increased risks of coronary heart disease (CHD) mortality and incident atrial fibrillation (AF). A large international investigation found that participants with subclinical hyperthyroidism had a 14.5% risk of total mortality and a 41.5% risk for AF. Risks for CHD mortality and AF were highest among those with thyrotopin levels lower than 0.10 mIU/L.

Abstract: Archives of Internal Medicine, May 28, 2012.