Abstract. The paper describes the features of in silico simulation of fluid flows of variable viscosity in the study of prosthetic heart valves. Computer modeling and its verification were performed on the example of  the bioprosthesis "UniLine" (Russia) used in modern cardio-surgical practice. A spatial model of the object of investigation was obtained by the method of computer microtomography, followed by the reconstruction of the primitive grid in two-dimensional sections. In the numerical experiment, the immersed boundary method was used. Herein the interaction of a solid and a liquid as well as the impact of mechanics of deformation of the elements of the prosthesis, such as the winged apparatus, were taken into account. Verification of the calculation algorithm was performed in the pulsating flow setup in conditions of simulating the physiological parameters of hydrodynamics similar to those used in silico. In general, the results of the simulation are consistent with the quantitative and qualitative data of the hydrodynamic experiment. Thus, in the numerical simulation, a pressure gradient of 3.0 ± 1.1 mmHg was obtained, an effective orifice area of 2.8 cm², a regurgitation volume of 0.1 ml/min. The experimental evaluation has shown the similar indicators: 6.5 ± 3.6 mmHg, 2.3 ± 0.6 cm², 3.1 ± 1.7 ml/min, respectively. The described method demonstrates its promise and can  be used in design and research tasks.