The patient was a 52-year-old woman who suffered from mitral valve regurgitation due to torn chordae. Mitral valve replacement (Medtronic-Hall 27 mm) was performed on Jan. 30, 1990. Immediately after the operation cardiac pacing was necessary for bradycardia, but one hour later cardiac rhythm changed to atrial fibrillation and the patient received an injection of verapamil. After the treatment of tachycardia, electro-mechanical dissociation (EMD) appeared on monitor. Bed side M-mode echocardiogram disclosed a restriction of the disc opening, but abnormal structures were not detected by B-mode echocardiogram. By repeated echocardiogram, the disc opening was normally demonstrated on M-mode, but B-mode showed an abnormally high echo structure in the left ventricle just below the prosthetic valve. Under the diagnosis of stuck valve in the closed position due to remnants of chordae, reoperation was performed. An eight mm remnant of chorda was found on the posteromedial side of the posterior leaflet, and it was supposed that the compression of the remnant between the disc and the valve ring restricted the valve opening. The remnant was resected through the large orifice of the Medtronic-Hall valve. After the reoperation, EMD was not detected and prosthetic valve insufficiency was not noted on echocardiogram. The patient left the hospital in a good condition three weeks after MVR.