Abstract: An implantable electronic unit (1, 30, 50), in particular a cardiac pacemaker, having at least one substantially socket-shaped connecting arrangement (3, 32, 33, 52, 53) arranged in the header (2, 31, 51) for a plug disposed at the proximal end of an electrode line (4, 34, 35, 54, 55), a plug receiving means (7, 60, 61) having a contact element (8, 20, 37, 38, 58, 59) for the deferent pole (6, 39, 40, 56, 57) of the plug, wherein the connecting arrangement includes a locking device (15) which secures the fit of the plug in relation to a tensile force acting in the axial direction and which can be operated by a hand lever (11) on the outside of the header.