A device (10) for warming infusion or transfusion fluids by an exothermic reaction of a reactive liquid, including at least one reaction chamber (11) containing a trigger, and a passageway (12) extending through said reaction chamber (11) for movement of said infusion or transfusion fluids therethrough, wherein the reactive liquid is introduced into said reaction chamber (11), being at least partially evacuated of air, to thereby initiate said exothermic reaction.
