Abstract: A flow circuit, such as a blood loop or in vitro closed-loop pump-driven circulation system for blood or other fluid including a heat exchange assembly that maintains a temperature of a sample fluid at body temperature. In one embodiment, the flow circuit is vertically oriented. In one embodiment, the flow circuit is an in vitro closed-loop blood circulation system comprises: a first closed-loop fluid flow path containing a warming fluid circulated therein and including a vertically oriented housing assembly; and a second closed-loop fluid flow path containing a sample fluid circulated therein, the first closed-loop fluid flow path and the second closed-loop fluid flow path being in a thermal exchange relationship with each other, at least a portion of the second closed-loop fluid flow path being vertically suspended from the vertically oriented housing assembly.