Device adapted to deliver fluids, in particular medicines, under pressure, comprising a receptacle 1 of variable volume in a form or shape of a pouch or flexible container of general cylindrical shape with exclusively longitudinal pleats 2 containing the fluid under pressure to be delivered and equipped with an actuator C permitting to open a valve 15a, 15b, to enable the aforementioned fluid to be delivered, the whole being located inside a receptacle 4 capable of resisting to an elevated internal pressure, the internal volume of this last receptacle comprised between its wall and the receptacle of variable volume being filled with a neutral gas under a pressure sufficient to exert on the receptacle of variable volume a pneumatic constraint sufficient to permit the delivery of the therein contained fluid when the above-said valve permitting the said delivery is operated by the aforementioned actuator C.