During a 10-year period, we have encountered 6 patients (mean age, 61.2 years) with left ventricular rupture following mitral valve replacement, with an overall incidence of 1.8 percent. Four patients had early rupture, one had delayed rupture, and one had late rupture with a false aneurysm formation. Among four patients with early rupture, there were two patients with external repair by using a large ventricular patch and two patients with internal and the external repair by removing the prosthetic valve and patching both the inside and outside of the ventricle. In a patient with delayed rupture, bleeding from an epicardial hematoma was recognized along the atrioventricular groove in the intensive care unit. It was possible to control bleeding by packing the gauze, hemostatic cellulose [Surgical], and fibrin glue. Late rupture was recognized as a false aneurysm; however, there were no clinical symptoms. All patients survived the surgery, but two patients with early rupture subsequently died. One of these died of renal failure and the other died of multiple organ failure. The sites of rupture in all patients were in accordance with type 1 rupture (Treasure's classification); however, an autopsy review demonstrated the initial laceration in one case was recognized in the membranous septum 5 mm below the mitral ring and extended to the posterior atrioventricular groove. These findings suggest that the injury in the anterior mitral annulus could lead to type 1 rupture, although in the posterior mitral annulus more commonly. Since 1987, we have preserved the posterior leaflet with attached chordae when the mitral valve was fragile and myxomatous. As a result, no instances of left ventricular rupture were encountered.