Abstract: A cardiotomy reservoir which employs an inner wall structure which defines a central receiving chamber. The receiving chamber wall is tapered inwardly to provide a smooth blood flow along an arcuate imperforate portion which extends from the top to the bottom thereof into the blood receiving chamber. Apertures in another arcuate portion of the wall member allow fluid communication between the receiving chamber and the blood treatment element. Blood flow directing means direct blood entering the inlet port of the device downward toward the bottom of the receiving chamber along the imperforate portion of the inner wall so that the inflowing blood does not splash and has low turbulence.