Described is a blood processing apparatus with a blood flow path and a heat exchanger fluid flow path overlapping the a heat exchanger chamber, in which the blood flows generally from a first end to a second end of the blood processing apparatus, and the heat exchanger fluid flows generally from the second end to the first end. Such "counter" or "countercurrent" flow improves heat transfer between the blood and the heat exchanger fluid. The blood processing apparatus includes a housing, a blood inlet, a heat exchanger fluid inlet and a heat exchanger fluid outlet, a heat exchanger core, a cylindrical shell having an annular shell aperture, a blood flow distributor, and a central chamber in fluid communication to a fluid flow distributor.
