The circulatory system of Herdmania includes heart and pericardium, blood vessels and blood. The blood is having a light reddish vacuole and transparent that is colourless plasma, many pigmented and non-pigmented corpuscles, and a few colourless amoeboid leucocytes. Lying below the right gonad is a tubular, elongated pericardium with thick non-contractile wall. The heart is attached along its whole length to the pericardium by a thin connective tissue flap. There are no true blood vessels in most ascidians, but they are well developed in Herdmania.