An assembly for reshaping a cardiac ventricle in a patient comprising an implantable device for reshaping a ventricle comprising a tether, a non-implantable tool which is detachably connectable to said implantable device and has a proximal portion and a distal portion opposite to said proximal portion; the implantable device further comprises an active anchor adapted to be detachably connected to the distal portion of the tool; the active anchor comprises an abutment portion adapted to abut against a structure of the ventricle; the active anchor of the implantable device comprises an adjustment device adapted to adjust the tensional state of the tether; the distal portion of the tool comprises an adjustment key adapted to cooperate with the adjustment device of the active anchor; the proximal portion of the tool comprises a maneuvering interface which is operatively connectable to said adjustment key for adjusting the tensional state of the tether by acting on the maneuvering interface of the proximal portion of the tool.