A prosthetic valve thrombus that occludes the blood flow or interferes with the valvular function is a rare, but life-threatening complication after prosthetic valve replacement. The patient's adherence with taking his anticoagulant medication is most critical. However, as seen in this presentation, the location of the prosthetic valve at the supra coronary sinus site may also be important. For the patient in this study, the blood flow and the speed of the flow through the valve were significantly reduced because the flow from the coronary sinus bypassed the prosthetic valve. This particular location of the prosthetic valve may be one of the risk factors that caused the thrombus. The right-sided prosthetic valve thrombus was successfully treated by thrombolysis with using urokinase, and there was no evidence of pulmonary embolism.