A transluminal sheath is advanced transfemorally into a left atrium of a heart of the subject. A surrounding-sheath is advanced out of a distal end of the transluminal sheath, into the atrium, and toward a commissure of the mitral valve. A helix is implanted at the mitral valve by advancing the helix out of the surrounding-sheath and through the commissure into a left ventricle of the subject, such that the helix wraps around at least some chordae tendineae of the mitral valve. A prosthetic valve is collapsed into a collapsed state, and subsequently to implanting the helix and collapsing the prosthetic valve, the prosthetic valve is advanced, in its collapsed state, through the transluminal sheath to the mitral valve. The prosthetic valve is implanted in the mitral valve by expanding it such that the helix facilitates anchoring of the prosthetic valve and sealing of the commissure.
