 Methods: The investigators will conduct a RCT in 185 patients with subclinical hypothyroidism who will be randomly assigned to thyroxine or placebo with an average follow-up of 24 months from baseline 4 death and 17 withdrawal. The main outcome will be CV imaging modalities measured by echocardiography at the close-out visit. Transthoracic echocardiography will be performed for the assessment of diastolic function abnormalities of the pulsed wave mitral valve inflow pattern and mitral annulus tissue velocities, left atrial volume index, left ventricular LV mass index and cardiac systolic function LV ejection fraction and regional function. Ultrasound of carotid intima media thickness CIMT will be used to assess subclinical atherosclerosis and plaque burden. All images will be centralized at the core lab for a blinded and standardized interpretation. 