A microlead implantable in a patient's venous, arterial or lymphatic networks for the detection and/or stimulation of tissue. The microlead has a diameter at most equal to 2 French (0.66 mm) and comprises at least one microcable (40) comprising a core cable (11) and an insulation layer (20) partially surrounding the core. The core is formed of a plurality of strands, and has a composite structure comprising a structuring material having high fatigue resistance, and a radiopaque material. A denuded area (30) is formed in the isolation layer (20) so as to form at least one electrode for stimulation detection. The microlead is shaped at the electrodes (30) according to at least one electrical contact and mechanical stabilization preshape, and has a gradual decrease of rigidity along the microlead between its proximal portion and its distal portion.