Final answer:
The statement is True, as the SA node fires more rapidly at higher body temperatures, increasing the heart rate and cardiac output to meet the body's higher metabolic demands.
Step-by-step explanation:
The statement that the sinoatrial (SA) node fires more rapidly at higher body temperatures, increasing cardiac output, is True. The SA node, located in the right atrium, is responsible for setting the pace of the heartbeat by initiating an electrical impulse that travels through the heart, causing it to contract. An increase in body temperature can lead to an increase in the metabolic rate, which typically increases the rate of depolarization in the SA node, resulting in a faster heart rate.
This, in turn, raises cardiac output to meet the body's increased metabolic demands. Conversely, a decrease in body temperature can lead to a slowing of the heart rate. As such, the rate at which the SA node fires is a critical factor in regulating not only the heart rate but also the overall cardiac output.