Stretchable conductors can have important application in wearable electronics. We prepared stretchable conductors by blending poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS, a conductive polymer) and elastomeric waterborne polyurethane (WPU) and demonstrated the application of the blends for thermotherapy and electromagnetic interference (EMI) shielding. Wearable heaters were fabricated by using the stretchable PEDOT:PSS/WPU blends. rGO was mixed into the to improve the temperature uniformity because rGO has high thermal conductivity while the polymers have very low thermal conductivity. The heater shows stable heating behavior under repetitive voltage on/off cycles, and the temperature remains almost unchanged under a tensile strain of up to 30%. The devices can be comfortably attached to the skin of humans, for example on the wrist, and they exhibit a uniform and stable heating profile even under mechanical disturbance. In addition, the PEDOT:PSS/WPU blends can be investigated for EMI shielding. Flexible or even stretchable electromagnetic interference (EMI) shielding materials with high performance are needed for wearable electronic systems. The PEDOT:PSS/WPU blends can exhibit a high EMI shielding effectiveness (SE) of about 62 dB over the X-band frequency range at a film thickness of only 0.15 mm.