A 41-year-old man had undergone mitral valve replacement (On-X 27/29 mm) and tricuspid valve replacement (TVR) (On-X 31/33 mm) for infectious endocarditis of the mitral valve and severe tricuspid regurgitation 6 years ago. Postoperative echocardiography showed aortic regurgitation and perivalvular leakage of the prosthetic mitral valve and left ventricular (LV) septal perforation. He therefore underwent aortic valve replacement (On-X 25 mm), patch closure of a leak around the prosthetic mitral valve, direct closure of the LV septal perforation, and re-TVR (On-X 31/33 mm). After discharge, he was placed on anticoagulant therapy with warfarin (international normalized ratio of prothrombin time target : 2.0-2.5). Transthoracic echocardiography three and -a half years after the operation revealed an increased mean tricuspid valvular pressure gradient (14 mmHg) compared with that seen on an echocardiograph of previous year. Cine-fluoroscopy showed almost no movement of the leaflets of the mechanical tricuspid valve. Tricuspid valve thrombosis or pannus formation was suspected. He was placed on thrombolytic therapy using tissue plasminogen activator (monteplase 1.6 million units). Five days later, cine-fluoroscopy showed movement of the mechanical tricuspid valve leaflets, and echocardiography revealed recovery of the mean tricuspid valve pressure gradient (4 mmHg). Valvular thrombosis was diagnosed as the cause of the non-moving valve. Hemorrhagic and embolic complications were not observed. Thrombolytic therapy was extremely useful.