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.
Echidna is a type of primitive mammals that belongs to the group of monotremes (mammals that lay eggs). Genus Echidna consists of two species: short-beaked echidna and long-beaked echidna. Short-beaked echidna inhabits Australia and New Guinea, while long-beaked lives only in the highlands of New Guinea.