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.
Biology. Echidnas are the oldest surviving mammal on the planet today, with five sub species of short-beaked echidnas, as well as their close relatives, the long-beaked echidnas; found in New Guinea. There are four subspecies of short-beaked echidna found in Australia.iology. Echidnas are the oldest surviving mammal on the planet today, with five sub species of short-beaked echidnas, as well as their close relatives, the long-beaked echidnas; found in New Guinea. There are four subspecies of short-beaked echidna found in Australia.