The doll has a plug under the armpit where you plug the heating console in. It has an internal thermostat that will heat and maintain the temperature of the doll at the desired temperature. Once ready to use, you can unplug her and the heat will stay for 60-80 mins. The entire body of the doll will heat and the thermostat ensures that she doesn't overheat and melt.
Click here for a video illustration from WM Dolls.