Abstract: A positive temperature coefficient heater for enhancing the response time of thermal actuators is disclosed. The PTC heater is formed of a generally low resistance material that has an anomaly temperature above which the resistance of the heater increases dramatically. The anomaly temperature is chosen to substantially match the phase change temperature of a thermally expansive medium useful to power the actuator. The heater is self-regulating and provides a maximum surface area for heating the medium rapidly with a minimum of thermal mass and energy use. Preferably, the heater is formed of doped BaTiO.sub.3 in the general shape of an elongated annular cylinder.