Apparatus and method for simulating tracer interaction with living tissue. A chamber receives a fluid therein, and includes an inlet conduit for conducting the fluid into the chamber, an outlet conduit for conducting the fluid out of the chamber, a medium disposed within the chamber for modulating fluid flow, and a valve assembly for conducting the fluid into the inlet conduit. In some aspects, the fluid is a radiative tracer or a radiative washout fluid and the medium is configured to mimic a tissue, e.g., the heart, and portions thereof are capable of mimicking both normal and diseased tissues.