The purpose of this paper is to present in vitro and in vivo experimental evaluation of a new, artificial, bicuspid, aortic and venous valve. Valves were constructed from square stents with barbs covered by porcine small intestine submucosa (SIS). A valve 15 mm in diameter was tested in a flow model (2.5 l/min) with pressure measurement. A 100-ml rubber bag attached to a side arm of the flow model simulated heart ejection fraction. In acute (n=6) and short-term (n=3) experiments conducted in four swine and four dogs, valves ranging from 16-28 mm in diameter were placed into the ascending aorta through 10 F sheaths; three were placed subcoronary and six in a supracoronary position. Function and stability of the valves were studied with pressure measurements and aortograms. Three short-term animals were sacrificed for gross and histologic evaluation at one, two and four weeks respectively. In an acute experiment, venous valves with four barbs were placed into the IVC through an 8 F guiding catheter in three dogs. For longer-term testing, valves were placed into the IVCs and iliac veins of three young swine. The animals were followed up after two weeks with venograms, then were sacrificed for gross and histologic evaluation.