Giant pandas (Ailuropoda melanoleuca) are flagship species for conservation because of their endangered status and charismatic nature. Giant pandas are placed in the bear family (Urisidae) within the order Carnivora. They specialize on a diet of bamboo, yet retain a typical carnivore gastrointestinal tract. Low energy digestive efficiency (9.5–34%) was calculated from bamboo-only digestibility trials conducted on captive giant pandas. Huge amounts of bamboo are consumed to overcome inefficient extraction and thus obtain sufficient energy and nutrients. I designed this study to gain insights into giant panda energy balance by measuring heart rates during sleep, their primary means of conserving energy. Because heart rate is directly related to oxygen consumption, metabolism was assumed to decrease as heart rate lowers. To test my hypothesis that giant pandas exhibit hypometabolism during sleep for energy conservation, I obtained physiological data remotely using radar technology. A metabolic depression of 61.5% below resting was determined from 12 captive giant pandas. I compared mean heart rates of pandas to those measured in captive black bears (Ursus americanus) and brown bears (Ursus arctos) during a time of seasonal lethargy. After adjustment for body mass, giant-panda heart rates were lower than the other species. Levels of metabolic depression were 61.5%, 72.4%, and 69.3% below resting in giant pandas, black bears, and brown bears, respectively. Based on these data, giant pandas lower metabolism on a daily basis to levels similar to those of black and brown bears during their seasonal lethargy.