Abstract: The present invention relates to an apparatus for injecting infusion fluids into a patient at a controlled infusion rate. This apparatus is referred to as a "controlled autoinfuser". A preferred embodiment of the invention comprises a computer capable of using pressure volume and relationships to generate a control signal that will control the injection of infusion fluids into a patient. The present invention further comprises a method of controlling the injection of infusion fluids into a patient through the use of a microprocessor controlled autoinfuser as well as a method of injecting a preselected volume of infusion fluid into a patient within a preselected infusion time.