An implantable device (1) for injecting and/or extracting fluid either into or from an organ or vessel of the body of a human or animal patient, or into or from an inflatable and/or deflatable compartment of a surgical implant, said device (1) comprising a housing (2) within which there is formed a chamber (2A) designed to be connected to a catheter (3), said catheter (3) itself being designed to be connected either to said organ or vessel or to said compartment, the housing (2) comprising a proximal wall (4) and a distal wall (5) with a side wall (6) extending between them, said housing (2) including a puncture zone (7) designed to be capable of being pierced by a hollow needle (14) in order to inject and/or extract fluid into or from the chamber (2A), the device being characterized in that said puncture zone (7) is shaped so as to extend simultaneously at least over the proximal wall (4) and the side wall (6). The invention also relates to implantable sites for injecting and/or extracting fluid.