Affection of cardiovascular system is one of the most frequent and--especially in higher age groups--the most serious clinical manifestations of thyroid dysfunction. Moreover, diabetics, mainly type 2 diabetes patients, have a marked predisposition to cardiovascular diseases, especially to atherosclerosis and its visceral complications. Simultaneous occurrence of diabetes mellitus (DM) and thyroid dysfunctions involves a very high risk of development and progression of various forms of cardiovascular diseases. There are two basal aspects of the influence of hypothyreosis on cardiovascular system. Decreasing basal metabolism in the whole organism reduces requirements on the cardiovsuclar system. The second aspect of the influence of hypothyreosis on the cardiovascular system is its atherogenic effect. Hypothyreosis in diabetics accelerates the development of chronic, primarily macroangiopathic complications. As opposed to hypothyreosis, the clinical picture of which is not characterised by cardiovascular system disorders, cardiac involvement in patients with hyperthyreosis is more pronounced. In older diabetics hyperthyreosis is often manifested only by cardiovascular symptomatology. Subclinical hyperthyreosis in DM patients may stimulate cardiac function and increase the risk of atrial fibrillation.