Abstract: A catheter and method for heating or cooling a surrounding fluid in a feeding vessel in a vasculature of a patient. The catheter includes a heat transfer element shaped and arranged to create turbulence in a surrounding fluid. A guidewire tube runs substantially parallel to the axis of the catheter to receive a guidewire. The catheter may further have a temperature-monitoring device disposed at the distal tip of the guidewire. Feedback may further be provided to control the temperature of a source of working fluid. A method is also provided for selectively controlling the temperature of a selected volume of blood in a patient.