Eleven patients who had undergone total thyroidectomy for differentiated thyroid cancer and who were on chronic TSH-suppressive therapy with levothyroxine (L-T4), underwent 24-h Holter electrocardiogram and Doppler-echocardiography before and after acute recombinant human TSH (rhTSH) administration for disease staging. The treatment, which was generally well tolerated, did not affect circulating thyroid hormones levels, nor did it have measurable effects on heart rate, rhythm, left ventricular morphology, or systo-diastolic function. Notably, arterial blood pressure tended to be slightly reduced after rhTSH administration, although in no instance did the patients become frankly symptomatic. Our data demonstrate that rhTSH does not alter cardiovascular function acutely. Consequently, it can safely be used in the routine staging of patients affected by differentiated thyroid cancer.