Reptiles go with the flow when it comes to staying warm. But even though they do not generate warmth within, reptiles seem able to regulate the rate at which they warm and cool, to make the most of the free heat they pick up. They appear to increase their heart rate while warming, and lower it while cooling. But no one had ever systematically followed how a reptile's blood pressure and shunt systems respond when the animal's pulse races and slows until Gina Galli, Ted Taylor and Tobias Wang began monitoring fresh water turtle's cardiovascular system responses to fluctuating temperatures.

Fitting the animals with monitoring equipment to track their body temperature, heart rate, blood pressure and blood flow rates, the team gently warmed the animals under a lamp and recorded how the reptile's cardiovascular systems responded to the changing temperature.

Sure enough, as the animals warmed their hearts beat faster, but slowed again when the lamp was switched off and the animals cooled. Monitoring the turtle's blood pressure, the team found that it remained constant, despite the animal's racing pulse. The reptile had reduced the resistance in its systemic system as its heart raced, but increased it again as the animal's heart rate fell while cooling. The animal was able to regulate its blood pressure, to maintain a constant pressure despite its fluctuating heart rate.

Galli, G., Taylor, E. W. and Wang, T. (
). The cardiovascular responses of the freshwater turtle Trachemys scripta to warming and cooling.
J. Exp. Biol.