An assembly of devices intended to regulate a patient's body temperature by circulating a temperature-controlled fluid (e.g., saline solution) through a dedicated, closed-circuit catheter placed in the central venous system (CVS), to both heat and alternatively cool the patient's blood through the transfer of heat as it moves past the catheter. It typically consists of a powered unit that controls fluid temperature and circulation, a catheter with a membrane for heat transfer, temperature probes, and a start kit. It may be used for body temperature regulation during surgery (e.g., cardiac surgery or neurosurgery), intensive care, or for fever management.