First, you need to understand what is a biological flap? What is a mechanical valve? A biologic valve is an artificial heart valve made by applying material from the body of another animal and processing it. The two most commonly used biologic materials are the bovine pericardial valve and the porcine aortic valve, and there is basically no difference in the service life of the two types of valves. Mechanical valves are prosthetic valves made of both nonmetallic and metallic materials and resemble familiar “doors” in structure, except that the door frame is circular and has one or two “doors” inside. A single flap is installed for one door, and a double flap for two doors. Most mechanical flaps are made of pyrolytic carbon, which is as strong and wear resistant as diamond, making them very strong and durable. What are the characteristics of biological flaps? Biologic valves are structurally similar to the human aortic and pulmonary valve structures and have similar hemodynamics to the human valve after implantation. About 3-6 months after implantation, the leaflet surface is covered with fibrin and vascular endothelial tissue, and the leaflet material is no longer in contact with the patient’s blood, avoiding the need for anticoagulation therapy as the blood clotting reaction is activated. However, since biomaterials have their own lifespan, it is generally believed that 7-10 years after surgery, the biologic flap begins to show some deterioration, although the function can be maintained; 15-20 years after surgery, the flap needs to be replaced again, which is the greatest shortcoming of biologic flaps. What are the causes of bioprosthetic valve destruction? The first is related to the implantation site. Because the pressure on the mitral valve (systolic pressure, commonly known as high pressure) is significantly higher than that on the aortic valve (diastolic pressure, commonly known as low pressure), the life expectancy of a bioprosthetic valve is slightly longer in the aortic than in the mitral valve. The second is age. Because children are in a phase of skeletal growth and development with active blood calcium metabolism, bioprosthetic valves are prone to earlier calcification and damage after implantation. Chronic renal insufficiency can also affect blood calcium metabolism and can occur as described above, although the process is relatively much slower. The heart rate is also too fast, which can accelerate valve breakdown. Finally, the quality of the biomaterial also has a significant impact on service life, although this factor is beyond the control of the physician or patient. Characteristics of Mechanical Valves The greatest advantage of mechanical valves is their durability. Based on experimental data alone, modern mechanical valves have a theoretical life expectancy of 50 years or more, so they can be used for patients of all ages. In addition, smaller mechanical valves (e.g., 19- or 21-gauge) have a significantly larger opening area than stented bioprosthetic valves of the same type, making them ideal for implantation in patients with smaller aortic rings; the frame structure of mechanical valves is also significantly lower than that of bioprosthetic valves, which are two additional advantages of mechanical valves. The biggest disadvantage of mechanical valves is the need for lifelong anticoagulation, which means that a daily dose of warfarin is required and the dose is adjusted according to the anticoagulation test results (INR). Daily anticoagulation is on the one hand cumbersome, and on the other hand, inadequate adjustment of the medication can easily lead to bleeding (over-anticoagulation) or thrombosis (under-anticoagulation). It is also more problematic to deal with patients on anticoagulation when internal bleeding (cerebral hemorrhage) occurs or when surgical treatment is required. Since warfarin can cause fetal malformations through the placenta, this is also a serious concern. Which is better, a unilobular or bilobular valve? In patients with larger annuli (especially aortic annuli), there is no significant difference between unilobular and bilobular valves, and there are isolated reports in the literature that unilobular valve hemodynamics appear to be more physiologically correct. However, in patients with smaller annuli, the bilobed valve has a larger opening area and better hemodynamics. In terms of anticoagulation therapy, the incidence of thrombosis and the consequences of thrombosis in mechanical valves are better with bilobed valves than with unilobed valves. Therefore, the clinical use of bileaflet valves is significantly higher than that of unileaflet valves, especially in the tricuspid position, where bileaflet valves are recommended. How do patients choose the right prosthetic valve for them? Once we know the respective characteristics of mechanical and bioprosthetic valves, we can choose them in relation to our own situation. Biologic valves are recommended for patients older than 65 years of age, with a flush heart rate and no atrial fibrillation, especially for patients older than 70 years of age. The bioprosthetic valve is also recommended for patients younger than 65 years of age with a life expectancy of 15-20 years or less. 2. Patients of childbearing age who wish to have children after surgery. Although it is still possible to attempt to apply heparin instead of warfarin for pregnancy after replacement of the mechanical flap, there is still a risk of malformation and bleeding and embolism, though. Therefore, it is strongly recommended that women who are planning to become pregnant opt for a biologic flap. 3. Biologic flaps are recommended for patients with bleeding tendencies. This includes patients with bleeding qualities, bleeding disorders, and other reasons for not receiving long-term anticoagulation therapy. 4. The bioprosthetic valve is recommended for patients who are unable to undergo anticoagulation due to geographic or medical restrictions. 5. Biologic valves are also recommended for patients with tricuspid valve replacement. 6. For patients in whom all conditions are suitable or require replacement of the bioprosthetic valve, but who have a small aortic annulus and aortic development, the application of a stentless valve for aortic root replacement may be considered. Mechanical valves are recommended in patients younger than 65 years of age with no contraindications to anticoagulation, particularly in patients with preoperative persistent atrial fibrillation and multivalvular lesions. 2. Patients who are not suitable for implantation of a bioprosthetic valve. Patients with a small aortic root, for example, or with a small left ventricle and a poorly defined left ventricular outflow tract, in which case implantation of a bioprosthetic valve in the mitral position can often lead to secondary stenosis of the left ventricular outflow tract and support the use of a mechanical valve. 3. If the patient requires tricuspid valve replacement with a mechanical valve, it is recommended to choose a bileaflet valve and avoid the use of a unileaflet valve. Conclusion: The application of biological and mechanical valves is not absolute and can be determined by in-depth communication with the physician based on their own situation. In foreign countries, more than half of the flap replacement patients choose biological flaps, mainly because of the higher quality of life, relatively few postoperative complications, and no financial burden for reoperation. In China, on the contrary, more than half of the patients choose mechanical flaps, mainly because of economic problems, and also because of the fear of secondary surgery. However, with the gradual development of biologic flap technology, the service life of biologic flaps will be gradually extended, and the economic and conceptual changes of people will also gradually increase the use of biologic flaps.