an electrode an electronics compartment within the cans 3 and 4 can contain the electronic components necessary for operation of the biostimulator including a battery and a controller a helical fixation device 5 can extend through a passage in can 3 into and through header 2 as shown in some embodiments the fixation device 5 can comprise an electrode and in other embodiments a distal electrode can be separate from the helical fixation device other details of leadless biostimulators may found in the copending applications referenced above and incorporated by reference herein in the embodiment of fig1 a thermistor 7 can disposed in header 2 the thermistors can include at least two thermistors leads for electrically connecting the thermistors 7 to the controller of the leadless biostimulator in this embodiment at least one of the thermistor leads can extend through a feedthrough in can section 3 to a controller within the can the other thermistor lead may be electrically connected to the can or can alternatively pass through a feedthrough into the interior of the can in this embodiment thermistor 7 can be in contact with an interior surface of header 2 and thus can be in thermal contact with blood surrounding the biostimulator through header 2 the controller inside housing 6.