An indwelling RF catheter achieves warming of patients by dielectric heating of blood or other bodily fluids. In one example, the catheter is deployed in a suitable blood vessel, such as the inferior vena cava. The catheter design includes an emitter structure electrically coupled to an RF generator, which provides a source of RF power. The emitter structure, distally located upon the catheter, administers electromagnetic radiation to the blood within the patient, thereby creating heat due to the dielectric qualities of blood. As blood heated by the indwelling RF catheter courses through the patient's body, the patient's body is systemically warmed, raising the body core temperature.