Interest in the role of thyroid hormones (TH) in heart failure is steadily 
increasing due to evidence for a physiological, homeostatic role of TH and the 
effects of altered TH metabolism on the cardiovascular system, particularly in 
presence of heart failure. Experimental studies have shown that altered TH 
metabolism modifies cardiovascular homeostasis by inducing alterations of 
cardiac histology, cardiomyocyte morphology and gene expression and 
consequently, of diastolic and systolic myocardial function. Clinical studies 
have shown that mild forms of thyroid dysfunction, both primary (subclinical 
hypothyroidism and subclinical hyperthyroidism) and secondary (low T(3) 
syndrome) have negative prognostic impact in patients with heart failure. In 
these patients, the administration of synthetic triiodothyronine (T(3)) was well 
tolerated and induced significant improvement in cardiac function without 
increased heart rate and metabolic demand. Large multicenter, placebo-controlled 
prospective studies are necessary to evaluate the safety and prognostic effects 
of chronic treatment with TH replacement therapy in patients with heart failure. 
The article also discusses recent patents in this field.