Abstract: An apparatus for patient safety protection in a medical device with a heater. A heater configuration for a medical device, such as a haemodialysis machine, is disclosed in which a shock hazard to the patient from the heater elements due to a single fault condition is eliminated. The invention comprises an insulation layer formed between the heater elements and a grounded metal plate. A single fault condition is prevented from creating a shock hazard to the patient (which is considered to be the dialyser fluid) because any break down of the insulation layer which brings the heater elements 14 into contact with the grounded metal plate will result in a large current flowing to ground (rather than to the patient), thereby causing a fuse in the circuit to trip. Tripping of the fuse removes power from the heating elements, thereby preventing any further possibility of contact between the live electrical heater element and the dialyser fluid (i.e. the patient).