Abstract: A suture ring for a mechanical heart valve comprised of essentially three parts: a stiffening ring which fits over an outer surface of the heart valve; a knit fabric sewing cuff attached to the stiffening ring, and a locking ring for securing the stiffening ring to the heart valve. The preferred embodiment comprises a locking ring which is generally crescent-shaped in cross-section and has a split ring configuration. Radial expansion or contraction is a first mode of deformation for the locking ring. The stiffening ring and the valve body can be locked together because the locking ring is capable of deforming in a second mode with respect to thickness of the ring. In the case of the preferred embodiment, the locking ring deforms by a slight flattening of the cresent cross-section of the ring.