Subclinical thyrotoxicosis (ST) characterized by low serum TSH and normal FT₄ and FT₃ concentrations. ST may cause changes of geometry of heart and developments of diastolic dysfunction. Influence of ST on this evolutions depending on age of patients, duration of SТ, effect of TSH level is not clear. In present research the effects of ST on changes of EchoCG at a different age were studied. The present study includes 102 normotensive patients with ST without any CVD (the age of 20–60 years, 10 men and 92 women) The patients were examined echocardiography by standard method. The patients were distributed on 3 age-grades: 1st group (gr1) (n=22) – 20–35 years; 2-nd group (gr2) (n=32) - 35–45 years and 3-rd group (gr3) (n=48) - 45–60 years. The parameters EchoCG were normal in patients of gr1 and gr2: relative wall thickness (RWT) (0,34 ± 0,009 and 0,35 ± 0,01 cm), left atrial diameter (LAD) (3,8 ± 0,09 and 3,8 ± 0,07 cm), isovolumic relaxation time (IVRT) (93,8 ± 1,93 and 92,7 ± 3,1 msec) left ventricular mass index (LVMI) (83,6 ± 3,24 and 90,5 ± 5,1 g/m²). However, the mean RWT (0,41 ± 0,01 cm, p<0,05), LAD(4,1 ± 0,18 cm, p<0,05), IVRT(100,6 ± 4,1 msec, p<0,05) and LVMI (103,2 ± 7,3 g/m² p<0,05) in patients gr3 was higher than that in gr1 and gr2. The frequency of left ventricular hypertrophy (LVH) was in gr1 – 10%, in gr2 – 8,3%, in gr3 – 36,4%, left atrial enlargement (LAE) was in gr1 - 25%, in gr2 – 20,8%, in gr3 – 35,5%, diastolic dysfunction (DD) was in gr1 - 30%, in gr2 – 31,8%, in gr3 – 47,4%, increase pulmonal pressure >30 (IPP) was in gr1 – 19%, in gr2 - 59%, in gr3 - 19%. The level T3, T4 was highly positive correlated with LAD(r=0,32, p<0,05) and pLA (r=0,55, p<0,01) and level TSH was highly negative correlated with pLA(r=−0,31, p<0,05). The LVMI and IVRT were positive correlated both with age (r=0,49, p<0,01 and r=0,34, p<0,05) and level T3(r=0,32, p<0,05 and r=0,25, p<0,1). Specific attributes of influence of ST on a heart were appearanced of IPP, LAE and DD, which were meet at any age with high often. The LVH was less characterised at ST and frequency of its development at young age is similar as in a comparable population on age. Frequency of LVH was significantly higher in patients >45 years old.