A transluminal sheath is advanced into a femoral vein of a subject, through an inferior vena cava of the subject, into a right atrium of a heart of the subject, and transseptally into a left atrium of the heart. A surrounding-sheath is advanced out of a distal end of the transluminal sheath, into the left atrium, and toward a commissure of a mitral valve of the heart. A commissural helix is implanted at the commissure by advancing the commissural helix out of the surrounding-sheath and through the commissure into a left ventricle of the heart, such that the commissural helix wraps around at least some chordae tendineae at the commissure and facilitates sealing of the commissure. Subsequently to the implantation of the commissural helix, the surrounding-sheath is extracted from the heart. Other embodiments are also described.
