THE CROCODILIAN HEART AND CENTRAL HEMODYNAMICS

The crocodilian heart is completely divided into two atria and two ven tricles, resembling the arrangement in birds and mammals. However, in addition to the systemic aorta (right aorta, RAo) which emerges from t he left ventricle, there is a second aorta (left aorta, LAo) that leav es the right ventricle beside the common pulmonary artery. The two aor tae communicate immediately outside the values through a small apertur e, the foramen of Panizza. During diastole, the blood pressures in the RAo and LAo equalize through the foramen, and the pressure in the LAo therefore remains higher (under most circumstances) than that generat ed by the right ventricle. preventing the LAo valve from opening. Bloo d flow in the LAo is biphasic, with a reversal of blood flow in systol e due to the closure of the foramen of Panizza by the medial cusp of t he RAo valve. Under these circumstances net LAo flow is low, and due s olely to flow through the foramen. When peak systolic right ventricula r pressure rises above that in the LAo, the valve will open, producing a (partial)Pulmonary bypass (right-to-left shunt). This may occur dur ing pulmonary vasoconstriction, or when the systemic (and hence the LA o) blood pressure decreases.