An electrically-powered device designed for in-line heating of banked blood, blood products, intravenous (IV) solutions, and irrigation fluids, typically from about 4ºC to near body temperature (i.e., 35 to 37ºC) before infusion, through the application of radiation. The device includes a heater that uses electromagnetic radiation (e.g., radio-frequency, microwaves) to transmit heat to the infusion blood/fluid via a disposable set (e.g., pouch or cassette); it also includes temperature controls and/or alarms. The warmer is used to minimize adverse thermal reactions in the patient. It is typically mounted on an IV pole under the infusion bag; it does not infuse blood/fluid.