Diving Bradycardia in the Trained Dolphin

IT has been known for nearly a century that bradycardia is a common feature of the circulatory response to the asphyxia of diving. Heart slowing has been observed in a wide variety of both aquatic and terrestrial animals during submersion1–3. Several lines of evidence indicate that this bradycardia is associated with a decreased cardiac output and widespread arterial vasoconstriction with vastly diminished blood flow in viscera and skeletal...