Blood pressures and heart rates in swimming hagfish

1. 1. Ventral and dorsal aortic pressures and heart rates were measured in the New Zealand hagfish Eptatretus cirrhatus at rest, during forced exercise and on recovery from swimming. 2. 4. Blood pressures were higher than those reported for the Atlantic hagfish, Myxine glutinosa, but were considerably lower than equivalent pressures found in teleost and elasmobranch fish. 3. 3. The ventricular pressure pulse was always transmitted to the dorsal aorta and our evidence contradicts the view that branchial resistance is high in myxinoids. 4. 4. Heart rates and ventral aortic pressures were higher after 10 min swimming, but the changes were not marked. 5. 5. The tachycardia was continued into recovery. 6. 6. The absence of bradycardia when the fish was disturbed (startle reflex) and the smooth increases and falls in heart rates and pressures suggest that neural regulation of the heart is not important in swimming and that venous return may be the major factor determining cardiac function.