A system and method for measuring recirculation of blood in a catheter designed for implantation in a human is described. In one variation, the system comprises an artificial circulatory system and an ultrasonic detection device for measuring and comparing the density of a circulated blood simulant with a later introduced bolus saline. The system may be configured to simulate a human heart by providing the flow, pressure and dimensions of a typical human heart. In addition to simulating the circulatory system of a normal human heart, the system may also be configured to simulate particular negative conditions of a patient, such as stenotic condition, which would affect the recirculation measurement.