In this study, flexible transparent heaters with heating films made of indium tin oxide (ITO) are fabricated on plastic substrates. The optical transmittance of a representative flexible heater is above 90% in the visible and near infrared regions. The steady-state temperature is determined by the bias voltage and reaches about 180 degrees C at a bias voltage of 50 V. The heat-generating properties are nearly the same before and after the application of tensile strain. Furthermore, the defrosting ability is demonstrated using a block of dry-ice.