Abstract: A system for monitoring and controlling a temperature of a heating element in a thermodilution catheter to maintain it within safe physiological limits includes a calibration circuit, a device for controlling the supply of power to the system, a relay between the calibration circuit and the heating element for switching power therebetween, a transistorized voltage detecting circuit for determining whether power has been supplied to the calibration circuit, and a device responsive to transistorized voltage detecting circuit to remove power from the system. Also, a method for monitoring and controlling a temperature of a thermodilution catheter-mounted heating element including providing a calibration circuit, switching a supply of power to either the calibration circuit or the heating element, monitoring the supply of power to the calibration circuit, and removing power from either the calibration circuit or the heating element in response to the monitored power at the calibration circuit.