The device for the injection of fluids comprises: a substantially elongated hollow body adapted to contain a fluid to be administered and having an access opening formed at a first end, and a suction/dispensing mouth of the fluid formed at a second end opposite to the first end； a piston element sealingly accommodated inside the hollow body and sliding between the first end and the second end for the suction/dispensing of the fluid； and mixing means formed inside the hollow body and adapted to mix the fluid during the movement of the piston element between the first end and the second end.
