A system and method for mixing and delivering fluids such as contrast media and saline is disclosed including at least two fluid sources, a pump, a joining fluid path connecting the at least two fluid sources to an inlet to the pump, and a valve device in the fluid path upstream of the pump. The valve device includes an actuator adapted to restrict flow in at least one of respective fluid lines connecting the at least two fluid sources to the pump inlet. A patient interface device may be associated with an outlet of the pump. The valve device actuator is generally adapted to restrict the flow in at least one of the respective fluid lines such that an incremental positional change in valve device actuator position provides a substantially linear change in fluid mixture ratio of the fluids from the at least two fluid sources to the pump inlet.