Typical in vitro analysis of medical device performance occurs at room temperature (~70 degrees Fahrenheit). Effective evaluation requires at temperature studies for blood contacting medical devices for the following purposes: wear characteristics, thermal expansion, and temperature effects on sensors in the design. The task was to control the fluid within an ISO5198 hydraulic loop used to evaluate left ventricular assist devices at a given temperature between 95F and 105F. The design was to function within one degree Fahrenheit. This task was accomplished utilizing a microcontroller, the PowerSwitch Tail II, a DS18B20 waterproof temperature sensor, and an immersion heater. To manage heat loss from the piping section of the loop foam piping insulation was installed to all non-testing sections. The group was able to successfully thermally regulate temperature in the loop for a range of flow rates (2-10 LPM). The team utilized a pulsing control architecture to keep overshoot within the system to a minimum. The system takes approximately 6 mins to come to temperature with approximately a one degree overshoot. The longest recorded success of controlling the loop within a plus or minus one degree accuracy is approximately 2 hours. A computational model of the system was made using the thermofluid blocks of the Simulink Simscape foundation library. Approximated heat loss is roughly 70 W for the entire circuit, which equates to one degree Fahrenheit drop for every five minutes without heat input. The result of this design is a cost effective means of producing reflective in vivo thermal conditions.