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.
The echidna is best known for its amazing biology. Like the platypus, this unusual mammal lays eggs and suckles its young. The echidna and platypus are the only members of a primitive group of mammals known as monotremes.