A collapsible valve prosthesis (1) includes an armature (2) and a set of prosthetic valve leaflets (3a, 3b, 3c) supported by the armature (2). The armature (2) is expandable from a contracted condition to an expanded condition for anchoring at an annulus of a natural valve site, and includes a tubular intra-annular portion (2a) defining a blood flow lumen having an inflow side and an outflow side. The tubular intra-annular portion (2a) supports (202, 204, 206) the prosthetic valve leaflets (3a, 3b, 3c) in the blood flow lumen and is provided with outward formations (200) for coupling with the natural valve site. The armature includes an over-annular portion (2b) linked to the intra-annular portion (2a) to extend collar-like over the annulus of the natural valve site at the inflow side of the blood flow lumen. The armature may also include an under-annular portion to extend collar-like at the outflow side of the blood flow lumen. The prosthesis may permit mitral valve replacement (MVR) without removing the native valve leaflets and the chordae tendinae.
