We report a case of a 38-year-old woman with a prosthetic mitral valve who presented with multiple embolic events. Transesophageal echocardiography was used to diagnose nonobstructive thrombi on the prosthetic valve. She underwent successful thrombolytic therapy. The patient was discovered to be in a hypercoagulable state, which probably was caused by the concomitant use of phenytoin. We review the literature for diagnosis and treatment of nonobstructive prosthetic valve thrombosis.