Flat fibrin thrombus deposition on tissue valve after aortic valve replacement.

Bioprosthetic valves have a lower thrombogenicity than mechanical valves, thus long-term systemic anticoagulation can be avoided. Herein, we present an extremely rare case of fibrin thrombus formation on tissue valve, which was observed during the second operation 2 years after the initial operation by chance. This report gives us a word of caution regarding the thrombus formation on the bioprosthetic valves that could be unaware of the presence for the long term.