Pathobiochemical mechanisms which participate in the rejection of transplanted heart are not fully clarified. A significant role in this process can be played by endogenous antioxidants, especially coenzyme Q10 which aside from its antioxidative properties is inevitable for cellular bioenergy. The authors investigated the concentration of Q10 alpha-tocopherol in endomyocardial biopsies in the blood in 11 patients from 1 to 9 years of age after transplantation of the heart (HTx-pat) examined in UKVCH in Bratislava who were compared with the group of 13 patients with cardiopathies of unclear origin (KPNP-pat) as possible candidates for transplantation. They detected a decreased concentration of coenzyme Q10 in the myocardium and blood of HTx-patients. Levels of alpha-to-copherol in the myocardium were identical in both groups, in plasma they were higher in patients after HTx. The authors suppose that the levels of coenzyme Q10 in patients after HTx can be influenced by an increased production of free oxygen radicals during rejection episodes, as well as immunosuppressive therapy, and indicate to the possible consequences of this decrease. The presented results provide the first information on the levels of coenzyme Q14 and alpha-tocopherol in patients after transplantation of the heart, registered and controlled in the Slovak Republic. They can contribute to the clarification of some pathobiochemical mechanisms of rejection, respectively to their therapeutic effect. (Fig. 2, Ref. 16.).