Apparatus for warming medical infusion fluids includes a heat pipe (12) warmed by an electrical heater (17) at one end. A replaceable fluid flow path (20) of helical configuration extends along the heat pipe (12) and is formed between an inner, thermally-conductive sleeve (21) with a helical profile and an outer insulative sleeve (26). An inlet (3) to the flow path (20) is located adjacent the heater (17), the outlet (4) being at the opposite end of the heat pipe (12). The inlet (3) is connected to a suspended saline bag (1) and the outlet (4) connects via tubing (5) to a catheter (6) inserted in a blood vessel. A temperature sensor (18) in the outlet tubing (5) provides a feedback output to a control unit (11) that controls operation of the heater (17) to maintain a stable temperature.
