The heart is enclosed in the pericardium, and consists of a median elongated ventricle and a pair of lateral auricles, so that the structure somewhat resembles that in the Lamellibranchiata.
The openings of the auricles into the ventricle vary in different forms. In many of the lower forms (Lepidopleuridae, Mopalidae, Ischnochitonidae) the opening on each side is single and anterior.
In the true Chitonidae there are generally two apertures on each side, and in two species three or four, another instance of the tendency to metameric repetition in the group. The auricles are connected with one another posteriorly behind the ventricle.
In Nautilus two pairs of auricles are present, corresponding with the two pairs of ctenidia.
Some blood, however, enters the auricles directly from the mantle, without passing through the ctenidia.