Cardiovascular consequences of thyroid diseases, their prevalence and treatment, particularly in cases with subclinical hyper- and hypothyroidism. The aim of the study was to draw attention to an association between the thyroid and cardiovascular diseases. The main topic was to lay emphasis on the importance of cardiovascular diseases caused by subclinical hyper- and hypothyroidism in the relation to the practice. The subclinical states precede the overt hyper- and hypothyroidism, and they are often present during their treatments. The changes in the levels of thyrotropin demonstrating subclinical thyroid diseases, could be detected in different non-thyroid diseases and resulted from the effect of some drugs. Particularly, the subclinical thyroid diseases become more frequent in older age. In the background of the high prevalences of atrial fibrillation, hypertension and psychosomatic events subclinical hyperthyroidism could be revealed. Subclinical hypothyroidism is characterized by an increased prevalence of elevated serum lipid levels, atherosclerosis, ischemic heart disease and hypertension often associating with the presence of anti-thyroid antibodies. It is important to reveal subclinical thyroid diseases in time for the effective treatment and for stopping of the cardiovascular damages before manifestations of cardiovascular diseases. The paper gives advice for the practice and the rational management. At the end, a survey of the association between thyroid and heart diseases in own department of internal medicine at the last three years is given.