A system for stimulation/defibrillation of the left ventricle endocardially or from a vein in the coronary system including: a lead body (10) having a lumen, a distal end (12) with an anchor (14) connectable to a wall of a heart chamber or of a vein of the coronary system, and a proximal side with a connector (22) having a first terminal (26). The lumen of the lead houses a microcable (28) with an active free part (30) that emerges from the distal end. An insert (38) formed on the lead body includes a first electrical connection to the first terminal (26) of the connector, and a coupler selectively movable between (i) a released position wherein the microcable is free to slide in lumen of the lead body, and (ii) a closed position, wherein the microcable is both mechanically immobilized in the lead body and electrically connected to first electrical connection.
