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.
A rare and curious animal, the eastern long-beaked echidna belongs to an incredibly distinct group of mammals, the monotremes. Like all mammals, the monotremes (the echidnas and the platypus), have fur and produce milk to nourish their young, but uniquely, these mammals lay eggs rather than giving birth to live young .