Embodiments of the present invention relate generally to heat-exchanger systems that can be used to heat or cool a fluid such as blood. Pod pumps that provide low shear and low turbulence may be used in such systems, particularly for systems that pump blood. A certain heat-exchanger system used to heat blood or other fluids may be used to provide whole-body hyperthermic treatments or regional hyperthermic chemotherapy treatments. A disposable unit may be used to separate the fluid path from the fluid control systems. The disposable unit typically includes a heat-exchanger component that is received by a corresponding heat exchanger in a base unit. Fluid pumped through the heat-exchanger component is heated by the heat exchanger.