An assembly includes a medical device provided with an anchoring member adapted to penetrate tissue of a cavity of the heart. The assembly further includes an implantation accessory including an elongated tubular element provided with a fastening mechanism for handling and guiding the medical device to an implantation site. The fastening mechanism includes an elastic deformable component cooperating with a rigid component, that is able to disconnect the medical device from the tubular element under the effect of a rotation exerted to the tubular element. The elastic deformable component cooperates with the rigid component such that the elastic deformable component exerts on the latter a radial constriction effect, and the elastic component and the rigid component being disconnected under the combined effect of a torsion torque and a traction exerted to the elastic deformable component, to thereby reduce the radial constriction until release of the rigid component.
