A device for injecting contrast agent includes a supply line with a pressure regulator and leading to a soft injection bag in fluid communication with the supply line and with a catheter. The device also includes a pair of clamping plates acting on the injection bag and arranged on opposite sides of the injection bag. The clamping plates can be moves away from and close to each other. The device also includes a pair of inflatable compression bags. The compression bags are inflated with compressed air and act on corresponding clamping to plates to force the clamping plates to move close to each other and thus compress the injection bag. According to a method of the invention, the injection bag is filled from the source through the pressure regulator and a constant volume load container, and a contrast agent is supplied from the injection bag by gradually compressing the injection bag.
