Abstract: The replacement device according to the invention makes it possible to replace at least one natural chord (19) making up the mitral valve, said natural chord normally being connected by one end to a pillar (20) formed by a muscular relief on the cardiac wall and, by another end, to a component leaflet (14) of the valve. The replacement device comprises a base (31) that can be fastened on a pillar (20) and on which at least one pair (P3) of chords (34) with predefined lengths are mounted that are suitable for being fastened on the leaflet (14) of the valve. Each pair (P3) of chords is configured in a loop provided with an end reinforcement for fastening on the leaflet (14) of the valve (12) opposite the base (31). The invention also relates to a kit comprising at least two replacement devices.