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.
1 : a reddish-brown dye obtained from leaves of the henna plant and used especially on hair and in temporary tattoos. 2 : an Old World tropical shrub or small tree (Lawsonia inermis) of the loosestrife family with small opposite leaves and panicles of fragrant usually white flowers.