A delivery assembly for a machine for preparing liquids product by means of cartridges includes: an injector device, to let water and/or steam under pressure in the cartridge, an infusion chamber, facing the injector device and capable of receiving one said cartridge, retention element, capable of maintaining the cartridge in a position substantially coaxial to the infusion chamber and the injector device. The retention elements having: a support element of the cartridge, sustained in a displaceable way by the injector device in a part thereof that generally faces towards the outlet passage; and guiding elements mounted in a fixed position at generally opposite side parts of the injector device, that frontally protrude from the injector device and are capable of laterally constraining the cartridge to guide it until a position substantially coaxial to the infusion chamber.