A stimulation/defibrillation epicardial lead unit, for the stimulation/ defibrillation of a heart cavity in combination with a generator of an active implantable medical device, in particular a pacemaker, a resynchronizer or a defibrillator, this unit comprising: - a stimulation/defibrillation epicardial lead of the screw lead type, including:. a lead body with a sheath made of a deformable material;. on the distal side, a lead head with a stimulation/defibrillation electrode and a protruding, helical, anchoring screw, adapted to enter into the external wall of the myocardium under the effect of a screwing movement imparted to the lead head; and. on the proximal side, means for the coupling to the generator of the medical device, and - a removable guide-catheter for insertion of the epicardial lead, adapted to be introduced in the pericardial space, this guide-catheter comprising a hollow tube, open at its two ends, with a central lumen into which the lead is able to be introduced and moved in translation inside the guide-catheter, first up to a retracted position where the lead head levels with the distal-side outlet of the guide-catheter lumen, then up to an extended position where the lead head, with the anchoring screw, emerges from this outlet, and the hollow tube of the guide-catheter being a preformed tube, elastically deformable and relatively stiffer than the sheath of the lead body, and showing, in the absence of stress, two successive bends (26, 28) inscribed in two distinct respective surfaces (30, 32), this unit being characterized in that: - the lead is a monodiameter lead, with the helical anchoring screw continuing axially the lead head; - said two successive bends (26, 28) are inscribed in a parallelepipedal volume with a size comprised between 15x10x5 mm and 25x15x5 mm; - the less distal bend of said two successive bends (26, 28) is a bend having an overall size, in the plane, of 15 to 25 mm by 10 to 15 mm, so as to follow the natural bend of the pericardial space during the progression of the guide-catheter and to provide, once the site of implantation chosen, a bearing of the lead body against the external wall of the pericardial space; and - the more distal bend of said two successive bends (26, 28) is a bend having an overall size, in elevation, of 10 to 15 mm by 5 mm at most, so as to allow, once the site of implantation chose, an orientation of the end of the guide-catheter tube according to a predefined attack angle in the direction of the external wall of the myocardium, and a holding of the axis of the anchoring screw in this same direction during a combined movement of screwing and displacement of the lead head towards the extended position. - a stimulation/defibrillation epicardial lead of the screw lead type, including:. a lead body with a sheath made of a deformable material;. on the distal side, a lead head with a stimulation/defibrillation electrode and a protruding, helical, anchoring screw, adapted to enter into the external wall of the myocardium under the effect of a screwing movement imparted to the lead head; and. on the proximal side, means for the coupling to the generator of the medical device, and. a lead body with a sheath made of a deformable material;. on the distal side, a lead head with a stimulation/defibrillation electrode and a protruding, helical, anchoring screw, adapted to enter into the external wall of the myocardium under the effect of a screwing movement imparted to the lead head; and. on the proximal side, means for the coupling to the generator of the medical device, and - a removable guide-catheter for insertion of the epicardial lead, adapted to be introduced in the pericardial space, this guide-catheter comprising a hollow tube, open at its two ends, with a central lumen into which the lead is able to be introduced and moved in translation inside the guide-catheter, first up to a retracted position where the lead head levels with the distal-side outlet of the guide-catheter lumen, then up to an extended position where the lead head, with the anchoring screw, emerges from this outlet, and the hollow tube of the guide-catheter being a preformed tube, elastically deformable and relatively stiffer than the sheath of the lead body, and showing, in the absence of stress, two successive bends (26, 28) inscribed in two distinct respective surfaces (30, 32), this unit being characterized in that: - the lead is a monodiameter lead, with the helical anchoring screw continuing axially the lead head; - said two successive bends (26, 28) are inscribed in a parallelepipedal volume with a size comprised between 15x10x5 mm and 25x15x5 mm; - the less distal bend of said two successive bends (26, 28) is a bend having an overall size, in the plane, of 15 to 25 mm by 10 to 15 mm, so as to follow the natural bend of the pericardial space during the progression of the guide-catheter and to provide, once the site of implantation chosen, a bearing of the lead body against the external wall of the pericardial space; and - the more distal bend of said two successive bends (26, 28) is a bend having an overall size, in elevation, of 10 to 15 mm by 5 mm at most, so as to allow, once the site of implantation chose, an orientation of the end of the guide-catheter tube according to a predefined attack angle in the direction of the external wall of the myocardium, and a holding of the axis of the anchoring screw in this same direction during a combined movement of screwing and displacement of the lead head towards the extended position.