Cardiac Function in the New Zealand Hagfish, Eptatretus cirrhatus

Evidence from respiratory and circulatory studies suggests that the hagfish genus Eptatretus is more adapted to an aerobic life and is more active than Myxine. This study aims to compare the cardiac dynamics of the two genera. The ECG of E. cirrhatus differed from that of fish in showing both a clear V wave and a PT deflection, the first caused by depolarization of the sinus venosus and the second by the repolarization of the atrium. Atrial and ventricular pressures were low; the ventral aortic average pressure was 16.3 ± 3.5 cm H₂O. Various cardiac parameters of the two hagfish are compared, and it is concluded that their hearts are very alike but differ from those of teleost fish in the slow rate of conduction in and contraction of the myocardium. These findings are discussed with reference to its anaerobic metabolism, its absence of a coronary circulation and T tubules, and the uncertain development of gap junctions between the myocardial cells.