Acquired heart diseases continue to remain one of the most common causes of cardiac mortality and morbidity. In the Russian Federation, open surgery treatment of acquired valvular heart diseases (AVHD) is performed in more than 40 regions by specialists from 92 healthcare organizations. Treating aortic or mitral valve disease using the UniLine biological prosthesis is expected to improve survival rates. Supposedly, in vivo the UniLine biological prosthesis will show optimal hemodynamic characteristics and high resistance to structural valve degeneration and infectious damage, thus lowering the risk of dysfunction. Moreover, the risk of repeated intervention due to dysfunction of the UniLine bioprosthesis should not exceed the risk of the primary implantation. Supposedly, in the case of dysfunction of UniLine bioprosthesis it would be possible to perform repeated replacement using valve-in-valve technique. The aim of the study is to assess the effectiveness, safety, durability of the UniLine epoxy-treated prosthesis and the long-term outcome of the treatment of isolated mitral and aortic valve diseases using this prosthesis. In accordance with the objectives and hypothesis, the following data will be analyzed: actuarial and linear survival rates (general and cardiac), non-lethal prosthesis-associated complications, prosthetic dysfunction and repeated interventions. Moreover, in vivo hemodynamic parameters of the prosthesis will be assessed: the area of the effective opening surface, peak and mean gradient of pressure and blood flow velocity. The study will be conducted at the Research Institute of Complex Issues of Cardiovascular Diseases. Study protocol received sponsorship approval and approval by Local Ethics Committee of the Research Institute and Research Coordinating Committee. The study will enroll patients who underwent isolated mitral or aortic valve replacement; transthoracic echocardiography will be conducted in all patients available for in-person visit.