An abnormal color flow signal originating from the prosthetic mitral valve and extending to the left atrium during diastole was seen in an 84-year-old female with St. Jude Medical valve replacement. This color flow signal was away from the transducer and was almost identical to the left ventricular inflow signal except for the direction. Cinefluoroscopy showed one of the leaflets fixed at systole while the other leaflet was mobile. After reinforcement of anticoagulant therapy, this abnormal color flow signal disappeared and motion of the both leaflets normalized. This color flow signal, presumably being a mirror image artifact of left ventricular inflow caused by the immobilized leaflet, could be a sign of one leaflet constriction in patients with St. Jude Medical valve replacement.