Despite anticoagulation, systemic embolization and anticoagulant-related hemorrhage are the major drawbacks of heart valve replacement with mechanical prostheses. Among many predisposing factors, inadequacy of anticoagulation is the most important one. Surgery can be reserved for patients who do not response to thrombolytic therapy, We have experienced 3 cases of prosthetic valve thrombosis treated by thrombolytic therapy by use of urokinase and heparin. Two patients fully recovered and returned to their employments and active lives but 1 patient,died of intracerebral hemorrhage and infarction. We report prosthetic valve thrombosis thrombolytic therapy with urokinase and heparin which was detected and serially followed by 2-dimensional echocardiography, cinefluoro copy, and monitoring of Swan-Ganz catherterized pressures.