Abstract
Heart rate of the fossorial mole rat at rest was compared with that of the similarsized white laboratory rat at normoxic, hypercapnic, and hypoxic conditions, in both thermoneutrality and cold. The heart rate of the mole rat in thermoneutrality and normoxia is 142 ± SD 15 min⁻¹. It is less than 0.5 the heart rate of the white rat and about 0.4 the expected value for a normal mammal of its size. The heart rate is arrhythmic. The heart rate of the mole rat is insensitive to hypercapnia up to . The mole rat is able to increase its heart rate in thermoneutrality and hypoxia down to of 32 torr. The mole rat is capable of maintaining a stable heart rate in cold and hypoxia (10 C; 41 torr), whereas the white rat cannot. The mole rat is prominent compared with other rodents in its ability to maintain and to increase heart rate in hypoxia.