β-Thromboglobulin (βTG), platelet factor 4 (PF4), fibrinopeptide A (FPA), lactic dehydrogenase (LDH), and platelet count were evaluated in patients with bioprostheses and prosthetic heart valves. βTG and PF4 were significantly elevated in both patient groups (p < 0.001), whereas FPA was normal. There was no significant difference in plasma concentrations of βTG and PF4 between patients with prosthetic heart valves and bioprostheses. LDH levels were significantly (p < 0.001) higher and platelet count lower (p < 0.001) in patients with prosthetic cardiac valves. The data indicate that bioprostheses do not cause haemolysis or activation of the coagulation system. The findings that the plasma concentration of platelet-specific proteins were elevated, support the assumption that both types of valves cause platelet dam