A system and method for implantation of an autonomous intracardiac capsule. The autonomous capsule includes a cylindrical body with an anchoring screw for penetrating a tissue wall, and at least one coupling finger radially projecting outwards. An implantation accessory includes a lead body and a helical guide, for guiding and driving by rotation the capsule. This helical guide is integral with the lead body, and its inner diameter is sufficient to contain that cylindrical body of the capsule therein. The helix direction of the helical guide is opposite to that of the anchoring screw such that continued rotational motion imparted on the lead body drives the anchoring screw into the target tissue and then emerges the capsule from the helical guide. The helical guide is resiliently compressible in axial direction, and its helix pitch is increased in the free distal end portion.