CONTEXT: Low-T(3) syndrome is a predictor of poor outcome in patients with 
cardiac dysfunction. The study aimed to assess the short-term effects of 
synthetic L-T(3) replacement therapy in patients with low-T(3) syndrome and 
ischemic or nonischemic dilated cardiomyopathy (DC).
DESIGN: A total of 20 clinically stable patients with ischemic (n = 12) or 
nonischemic (n = 8) DC were enrolled. There were 10 patients (average age 72 yr, 
range 66-77; median, 25-75th percentile) who underwent 3-d synthetic L-T(3) 
infusion (study group); the other 10 patients (average age 68 yr, range 64-71) 
underwent placebo infusion (control group). Clinical examination, 
electrocardiography, cardiac magnetic resonance, and bio-humoral profile (free 
thyroid hormones, TSH, plasma renin activity, aldosterone, noradrenaline, 
N-terminal-pro-B-Type natriuretic peptide, and IL-6) were assessed at baseline 
and after 3-d synthetic L-T(3) (initial dose: 20 microg/m(2) body surface.d) or 
placebo infusion.
RESULTS: After T(3) administration, free T(3) concentrations increased until 
reaching a plateau at 24-48 h (3.43, 3.20-3.84 vs. 1.74, 1.62-1.93 pg/ml; P = 
0.03) without side effects. Heart rate decreased significantly after T(3) 
infusion (63, 60-66 vs. 69, 60-76 beats per minute; P = 0.008). Plasma 
noradrenaline (347; 270-740 vs. 717, 413-808 pg/ml; P = 0.009), N-terminal 
pro-B-Type natriuretic peptide (3000, 438-4005 vs. 3940, 528-5628 pg/ml; P = 
0.02), and aldosterone (175, 152-229 vs. 231, 154-324 pg/ml; P = 0.047) 
significantly decreased after T(3) administration. Neurohormonal profile did not 
change after placebo infusion in the control group. After synthetic L-T(3) 
administration, left-ventricular end-diastolic volume (142, 132-161 vs. 133, 
114-158 ml/m(2) body surface; P = 0.02) and stroke volume (40, 34-44 vs. 35, 
28-39 ml/m(2) body surface; P = 0.01) increased, whereas external and 
intracardiac workload did not change.
CONCLUSIONS: In DC patients, short-term synthetic L-T(3) replacement therapy 
significantly improved neuroendocrine profile and ventricular performance. These 
data encourage further controlled trials with more patients and longer periods 
of synthetic L-T(3) administration.