Stenosis of the left ventricular outflow tract is one of the most frequent congenital cardiac anomalies in dogs. The subvalvular stenosis is described as a ring of fibrous tissue located in the left ventricular outflow tract immediately below the aortic valve. The best method of surgical treatment in dogs seems to be relief of the aortic obstruction with a ventricular aortic prosthesis. A new trileaflet valve manufactured out of polyurethane has been developed. For the conduit a woven Dacron graft has been used. In 5 male dogs a valved conduit was implanted between the apex of the left ventricle and the aorta thoracica without using hypothermia and/or cardiopulmonary bypass. Four dogs survived the surgical procedure and showed no clinical symptoms postoperatively. Blood flow through the conduit was demonstrated postoperatively by angiocardiography for a maximum of 22 days, the longest surviving time being 8 weeks. Trials for the replacement of the artificial valve in the conduit by a canine aortic allograft valve are in progress. Studies were done with the cryopreservation of fresh aortic valves. Sterilization, cryoconservation, and storage methods for the allograft are described.