Myoarchitecture and vascularization of the elasmobranch heart ventricle

The myoangioarchitecture of the elasmobranch heart ventricle is characterized by two specialized features: 1) a mixed type of musculature, with a compact outer layer (compacta) covering the inner trabecular core (spongiosa) of the wall; and 2) a coronary arterial supply derived from a hypobranchial source that is homologous with the coronaries of homeotherm vertebrates. Contrary to the previously accepted opinion that the coronaries supply the compacta whereas the spongiosa is supplied solely from the venous blood of the ventricular lumen (lacunary system), we demonstrate in a number of species that the coronary arterial tree ends directly within the ventricular lumen via impressive arterioluminal terminations (Thebesian vessels). Thus, there is a shunt from the oxygenated coronary blood to the lacunary venous system of the spongiosa. This myoarchitecture occurs only in the most active teleosts. It is present in all elasmobranchs, regardless of the ecophysiology or oxygen cardiac requirements of a particular species. The functional significance of this arterial arrangement thus represents a challenge for comparative cardiology and may help clarify the phylogenetic and physiological aspects of the vascularization of the fish heart.