At present, the use of bioprosthetic flaps generally accounts for about 30% abroad and about 22% in Europe. In China, due to the shortage of mechanical valves in the 1980s, the use of biologic valves accounted for about 70%, but due to some problems in quality control and the increase in cases of biologic valve failure after the 1990s, the use of mechanical valves is still the majority. Prosthetic valves are divided into two categories according to the materials used: one is all made of artificial materials called mechanical valves and the other is all or partly made of biological tissue called biological valves ① mechanical valve classification: all mechanical valves can be divided into peripheral flow (ball cage and disc cage valves) and central flow (oblique disc and double leaflet) according to their blood flow pattern. ② Classification of biological valves: Biological valves can be divided into two main categories, heterogeneous and homogeneous valves. The heterogeneous valves include porcine aortic valves and bovine pericardial valves; homogeneous valves include fresh homogeneous aortic valves, autologous broad fascial valves, and homogeneous dural valves. Advantages and disadvantages of biologic valves: Many investigators have compared the characteristics of two porcine biologic valves, the hancock and carpent infective endocarditis r-edwards, and overall, there were no significant differences in the short- and long-term efficacy of these valves. In a prospective trial with 10-year follow-up, 174 patients undergoing mitral or aortic valve replacement were randomly assigned to receive hancock and carpent infective endocarditis r-edwards porcine bioprosthetic valves, and the results showed no significant differences in patient survival, valve durability, or valve-related complications. These findings were confirmed in another trial in which 147 patients undergoing mitral valve replacement were randomized to receive either the carpent infected endocarditis r-edwards or hancock porcine bioprosthetic valves and were followed up at 10 years and found no significant differences in survival or valve-related complication rates between the two groups. To facilitate implantation, previous bioprosthetic valves were secured to stents, allowing a firm foundation for relatively soft tissue-based valves, but such stents and sutured rings significantly reduce eoa, so that tissue-based valves appear relatively narrow compared with mechanical valves. Recently, there has been significant interest in stentless bioprosthetic valves, which, like other tissue-based valves, have good hemodynamic performance and do not require anticoagulation. In one study, 245 patients implanted with toronto sv stentless valves (st jude medical) were followed for 3 years and found improvements in eoa and transvalvular pressure difference over time and a 14.3% reduction in left ventricular weight over the study period. As with all bioprosthetic valves, the major failure that occurs with stentless valves is valve regurgitation. 27% of the 200 patients who had a stentless aortic valve (prima edwards; baxter healthcare) placed had aortic valve insufficiency at 1 year, but only 1 had third-degree insufficiency. In another nonrandomized study, 150 patients were implanted with stentless bioprosthetic valves (prima edwards), conventional bioprosthetic valves, or homogeneous allogeneic valves Stentless valve replacement of the mitral valve is more difficult because the shape of the mitral annulus changes with the cardiac cycle and requires additional external forces to maintain the function of the stentless valve. This is an engineering challenge, and the initial solution is to first secure the stentless valve to the papillary muscle with an artificial tendon. Short-term success has been reported, but it is still in the experimental phase. Another tissue-based valve that has recently been applied is the homogeneous valve, which is a tissue-based valve (including aortic and pulmonary valves) taken from human cadavers, antimicrobially sterilized and cryopreserved. Homogeneous valves have many advantages, including low transvalvular pressure gradients and low incidence of infection, and can be used in patients with active endocarditis, although early thrombosis can occur and therefore anticoagulation is still required. Transplanting a homograft valve is much more difficult than transplanting a stent-fixed bioprosthetic valve and requires some surgical experience and skill. In two studies with 8 and 14 years of follow-up, only 17% and 14% of patients, respectively, had reoperation for structural degeneration of the homograft valve, primarily because of progressive worsening of the closure insufficiency. Another type of homogeneous aortic valve replacement uses an autologous pulmonary valve graft (ross) procedure. The procedure involves removal of the patient’s normal pulmonary valve (autograft valve), replacement of the patient’s aortic valve, and replacement of the removed pulmonary valve with a cryopreserved human pulmonary valve (homograft valve). This procedure has a number of advantages. First, both valves are tissue-based and therefore do not require anticoagulation. Second, autologous pulmonary valve grafts do not require antimicrobial sterilization or cryopreservation, are easily survived and grown, and have good durability. In a study of 195 patients, 89% of patients did not require reoperation after 5 years. Patients who received pulmonary artery autografts had similar hemodynamic performance and immediate and intermediate postoperative outcomes compared with aortic valve allograft replacement. However, there are three drawbacks to pulmonary artery autografting: first, the scope of the procedure is expanded from single to double valve replacement. Moreover, even if the autologous pulmonary valve functions well, there is a risk of tissue degeneration and homogeneous allograft pulmonary valve obstruction. Second, even with excellent surgical skills and rigorous patient enrollment, 20% of patients still require reoperation for pulmonary valve replacement after 20 years. In addition, 10-20% of patients after autologous valve transplantation develop aortic valve insufficiency of grade II or greater. Therefore, this approach requires long-term follow-up studies to determine the safety and durability of autologous pulmonary valve replacement.