In 47 patients blood traumatisation was checked after interventions on cardiac valves. The cases in question were: 34 implantations of valve prostheses, 10 valve reconstructions and 3 re-operations because of paravalvular leakages. The tested valve prostheses according to Starr-Edwards, Björk-Shiley and Beall revealed subclinical haemolyses of various degrees. In aortic position the values for Björk-Shirley prostheses showed advantages as compared to the Starr-Edwards valve. Of all tested valve types the Beall prostheses caused the highest blood traumatisation. Manifest haemolytic anaemia was found only in 3 cases, two of them showing paravalvular leakage. In the cases of double valve replacement performed with combined Starr-Edwards and Beall prostheses the haemolysis was only slightly higher than in cases of mitral valve replacement with Beall valves only. In three cases with paravalvular leakage the parameters of haemolysis increased very much, returning to normal in 2 patients after successful correction. The assessment of the parameters of blood traumatisation is indispensible for the choice and improvement of the different types of valves and essential for the diagnosis of paravalvular leakage as well as for the control after leakage repair.