An intravenous fluid heater is provided that is dimensioned so as to be wearable adjacent a patient's intravenous fluid infusion situs. In one embodiment, the heater includes a heat exchanger for defining a flow path through the heater for fluid to be infused via the infusion situs. At least one controllable heating element is provided for heating the fluid in the flow path by heat conduction thereto through the heat exchanger. Sensors are included for sensing respective temperatures of entering and exiting fluids of the flow path. A controller controls, based upon the temperatures of the exiting fluids, heating of the fluid in the flow path by the heating element so as to cause the fluid in the flow path to be substantially uniformly heated to a desired infusion temperature prior to exiting the heater.