Abstract: An in vitro tissue testing system especially useful for testing blood/tissue interactions. The system includes a tissue holding frame which forms a chamber between two flat pieces of tissue with a spacer plate therebetween. The spacer plate includes a reservoir aperture bordered on both sides by the opposed tissue pieces, and a mechanism for depressing portions of the tissue pieces inwardly into the chamber to propel blood from one side of the chamber to the other. The flow created simulates actual blood flow in a host system. The reservoir aperture may be hourglass shaped with circular end portions and a middle blood passageway. The actuating mechanism may include pistons for alternating contact with the tissue within the confines of the opposite reservoir end portions, thus propelling blood from one end portion to the other. The pistons may be driven by a plurality of eccentric cams on shafts coupled to a common drive motor.