Performance of the heat of the hagfish,Eptatretus cirrhatus.

The maximum power output of isolated perfused ventricles of the hafish (Eptatretus cirrhatus) averaged 0.367±0.031 mW g(-1) (n=9), considerably high than estimates for the heart of the Atlantic hagfish (Myxine glutinosa). Maximal minute volumes averaged 21.55±1.28 ml min(-1)kg(-1), with a mean stroke volume of 0.71±0.14 ml kg(-1) body weight, values which are similar to those reported for many teleost and elasmobranch hearts.Ventricular output showed the characteristic dependence upon atrial filling pressure up to an optimum filling pressure ofc. 4 mm Hg. At output pressures exceeding 14 mm Hg the stroke volume and power output fell sharply. At these afterloads, the ventral aorta remained distended following semilunar valve closure and so the volume of fluid ejected on ventricular systole was reduced. There was little change in the frequency of the heart as either input or output pressures were varied.