A heater cooler apparatus 1 for a perfusion system heat exchanger 26, where the heater-cooler apparatus 1 comprises a heater cooler device 10 and an antimicrobial fluid. The anti-microbial fluid may be a heater-cooler fluid 11. Heater-cooler apparatus 1 may further comprise an intermediate heat exchanger 40 between the heater-cooler device 10 and an intermediate passage 30, where the heater-cooler device 10 supplies the heater-cooler fluid 11 to intermediate heat exchanger 40, where the intermediate passage 30 supplies an intermediate fluid 31 to the perfusion system heat exchanger 26 and where the intermediate heat exchanger 40 permits heat exchange between the heater-cooler fluid 11 and the intermediate fluid 31, where the heater-cooler fluid 11 is fluidly isolated from the perfusion system heat exchanger 26. The antimicrobial fluid may be intermediate fluid 31. Preferably the antimicrobial fluid is biocidal. The antimicrobial fluid may comprise glycol. Also use of an antimicrobial fluid in an extracorporeal perfusion system and a method of setting the temperature of an extracorporeal fluid passing through a perfusion system heat exchanger. The provision of antimicrobial fluid is described as reducing risk of microbe contamination of an extracorporeal fluid and reducing the requirement for time consuming manual sterilisation procedures.
