The mitral valve and its supporting structures are normally flexible. Over time, however, if your valve tissue is replaced by calcium, the valve becomes stiffer because calcium is very hard and not very flexible. Severely calcified valves are like a plaster wall. When one tries to pound nails into a plaster wall, the plaster usually crumbles and falls apart. Similarly, when putting a new valve into hard calcium, the heart wall may not hold together very well. As a result, it may tear -- causing a rupture in the heart wall. Rupture of the heart wall with mitral valve replacement occurs rarely, or in approximately 1 out of 100 cases. If this happens, your surgeon will repair the rupture in the heart wall.