[Adaptive changes in the cardiac automatism of the sea otter Enhydra lutris].

Electrographic investigations in sea otters reveal acute decrease in the heart rate (to 1/2--1/8 of the normal rate) during diving. The longer the dive, the more intense the bradycardia. Each partial exhalation under water causes further decrease in the heart rate. The duration of cardiac cycles (R--R) increases mainly at the expense of the prolongation of diastole (T--P). Variations in the heart rate during submersion result from the increased vagal tone. Atropine injections abolish diving bradycardia. On surfacing, the animals exhibit a pronounced recovery tachycardia.