The cardiac output in Octopus dofleini has been measured, making use of the Fick principle.

The measurements were made on intact animals, resting or free-swimming, after previous chronic implantation of intravascular catheters for collection of blood samples.

The respiratory exchange was measured with a specially designed respirometer.

In addition to cardiac output the following parameters were measured or computed: oxygen consumption; oxygen tension, oxygen content and percentage saturation of venous and arterial blood; arterial pressure; heart rate; stroke volume and stroke work.

A detailed discussion of the results obtained is limited by the lack of comparable information for other invertebrates.

This work was supported by grant GB-358 from the National Science Foundation.