Background This preclinical study in sheep sought to demonstrate the initial safety and feasibility of a novel transcatheter mitral valve system (Mi-thos valve) composed of a self-expanding frame and a bovine pericardial tissue bioprosthesis.Methods The valve was implanted in 26 sheep using a transapical approach for short-and long-term evaluation.The technical feasibility,safety,durability,and valve function were evaluated during and 6 months after the procedure using intracardiac and transthoracic echocardiography,multisliced computed tomography,histological analysis,and electron microscopy.Results The success rate of valve implantation was 100％,and the immediate survival rate after surgery was 84％.Five animals died within 90 min after the development of the prosthetic valve due to an acute left ventricular outflow tract obstruction (n =2) and sudden intraoperative ventricular fibrillation (n =3).Twelve animals died within 1 month due to acute left heart dysfunction.Mild (n =5) and moderate (n =2) paravalvular leakage occurred in seven animals,and two moderate PVL animals died of chronic heart failure within three months.Multimodality imaging studies of the remaining seven animals showed excellent function and alignment of the valves,with no coronary artery obstruction,no left ventricular outflow tract obstruction,no severe transvalvular gradients and no paravalvular leakage.Macroscopic evaluation demonstrated stable,secure positioning of the valve,with full endothelialization of the valve leaflets without injury to the ventricular or atrial walls.Histological and electron microscopic examinations at six months showed no obvious macro-or microcalcification in the leaflets.Conclusions Preclinical studies indicate that transcatheter implantation of the Mi-thos valve is technically safe and feasible.The durability,functionality,and lack of leaflet calcification were all verified in animal experiments.The information from these preclinical studies will be applied to patient selection criteria and the first-in-human studies.