Medtronic Hancock (Standard Model) : These are gluteraldehyde preserved xenograft aortic valve, which are mounted. The modified orifice version (M-0) is one where the right coronary cusp (which in a porcine valve has a muscular ridge) is excised and replaced with another leaflet of a valve of the same size. A new variety of second generation Hancock valve in which the fixation pressure is zero and toludine blue is added to inhibit calcium deposition is now available.