Cardiac function was evaluated in rest and after exercise on a cycloergometer in 20 patients with essential hypertension (EH) aged 14 to 19 years and 12 age-matched healthy volunteers. Selected parameters of ECHO examination and mitral flow were assessed, including SV, CO, CI, %SF, EF, LIVDd, IVSd, LVPWd, LVMI, total peripheral vascular resistance, ESS, velocity of wave E. A and E/A index. In all cases, serum ET1 and NPY levels were measured in rest and after exercise, before and after 6-month enalapril therapy. The ETI serum level in hypertensive patients did not differ from controls, while the NPY level was significantly higher in hypertensives. Exercise did not affect the ETI serum concentration, however, it did increase the NPY level. Enalapril therapy had no effect on serum peptide concentrations. Correlation of the ETI serum level with ECHO parameters, including CO, Cl, SV, LIVDd, LVPWd, %SF, TPRI and wave E velocity, as well as correlation of NPY concentration with LIVDd, LVPWd, LVMI, ESS and wave E and A velocity may suggest that these peptides influence left ventricle function and structure disturbances in children with EH.