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.
Toxicodendron radicans, better known as poison ivy (older synonyms are Rhus toxicodendron and Rhus radicans), is a poisonous North American plant that is well known for its production of urushiol, a clear liquid compound found within the sap of the plant that causes an itching rash in most people who touch it.