['Thyroid hormone has important effects on the cardiovascular system. The consequences of episodes of acute hypothyroidism on cardiac function have been investigated in only a few studies, and their results are inconclusive. Our objective was to investigate the effects of acute hypothyroidism on cardiac function in patients with iatrogenically induced subclinical hyperthyroidism after treatment for differentiated thyroid carcinoma.', 'Fourteen patients with a history of differentiated thyroid carcinoma on thyroid-stimulating hormone (TSH)-suppressive thyroxine replacement therapy were studied. We assessed cardiac function before, and 1 and 4 weeks after withdrawal of thyroxine substitution. We measured serum levels of free thyroxine, triiodothyronine and TSH and used a new sophisticated Doppler echocardiography technique, tissue Doppler imaging (TDI), to assess detailed and quantitative assessment of systolic and diastolic cardiac function. Echocardiographic parameters in patients were compared to controls.', "Compared to controls, patients had higher left ventricular mass and wall thickness and decreased diastolic function during TSH-suppressive l-thyroxine substitution therapy. Thyroxine withdrawal resulted in a decrease in both early (E) and late (A) diastolic mitral inflow velocities, without impact on E/A ratio. Using TDI, late diastolic velocity (A') decreased without impact on E'/A' ratio. Left ventricular dimensions, wall thickness and mass did not change during thyroxine withdrawal."] Does short-term overt hypothyroidism induce discrete diastolic dysfunction in patients treated for differentiated thyroid carcinoma?