Congestive heart failure is the main cause of cardiovascular morbidity and mortality with more than one million hospitalizations per year. Dilated cardiomyopathy is one of the main causes of congestive heart failure characterized by diminished function of the left, right or both ventricles and ejection fraction less than 40%. Numerous studies reported that the diseases of thyroid gland among the patients with dilated cardiomiopathy were very frequent: with prevalence from 18% to 49%. The impaired thyroid gland function was found as primary cause of cardiomyopathy in 1% of patients. At the same time, among patients with terminal dilated cardiomyopathy, euthyroid sick syndrome was very frequent with low values of T3. According to our results, 29.4% of patients with dilated cardiomyopathy also had autoimmunity disorder of thyroid gland with present antithyroglobin and antimicrosomal antibodies. These patients had lower ejection fraction and worse prognosis. In American College of Cardiology/American Heart Association guidelines for the evaluation and treatment of the congestive heart failure, evaluation of thyroid gland function was recommended; but the evaluation of antitireoglobulin antibodies and free T3 and free T4 was also essential, as was calculation of their ratio. This is the way to discover the autoimmunity disorder of thyroid gland and/ or "euthyroid sick syndrome". In patients with dilated cardiomyopathy and low-T3 syndrome, short-term administration of thyroid hormones resulted in improvement of ejection fraction, diminishing of symptoms and better survival.