Aortic insufficiency (AI), also known as aortic regurgitation (AR), is the leaking of the aortic valve of the heart that causes blood to flow in the reverse direction during ventricular diastole, from the aorta into the left ventricle.
Definition of echidna. : a spiny-coated toothless burrowing nocturnal monotreme mammal (Tachyglossus aculeatus) of Australia, Tasmania, and New Guinea that has a long extensible tongue and long heavy claws and that feeds chiefly on ants; also : a related mammal (Zaglossus bruijni) of New Guinea having a longer snout and shorter spines.
There are two species of echidnas: the long-beaked echidna, which is confined to the highlands of New Guinea; and. the short-beaked echidna, which lives in Australia and New Guinea. The short-beaked echidna is the smaller of the species, and individuals vary in colour depending on their location.