UC San Diego

Although there are many studies describing the behavior/ecology of whales, little is known of their physiology. Furthermore, the limited data available regarding cardiac function in whales have been collected under atypical conditions. To address this, we applied electrocardiogram (ECG) recorders with a suction cup attachment technique to a killer whale (Orcinus orca), pilot whale (Globicephala macrorhynchus), and beluga whale (Delphinapterus leucas) to investigate heart rate regulation. The PR and QRS intervals of ECG signals were in the same range as previously published values in large mammals. Heart rates “at rest” in a pool were 83–140% of the allometrically predicted resting heart rates. Heart rates during swimming activities were higher than at rest in the killer whale and beluga whale, but lower in the pilot whale. Frequent fluctuations in apneic heart rate occurred during all activities, including rest and stationary submersions. We conclude that a) electrical impulse conduction in the hearts of whales does not scale allometrically as in small mammals, b) heart rates “at rest” can be elevated, probably secondary to non-fasting conditions, c) exercise does not always increase heart rate in whales, and d) beat-to-beat oscillations in apneic heart rate are common and can occur without exercise.