Prosthetic materials are used for right ventricular outflow tract (RVOT) reconstruction in cases of congenital heart defects with right ventricular outflow hypoplasia or atresia and for pulmonary valve replacement in the Ross procedure. This procedure is to replace the stenotic pulmonary heart valve such as hypoplastic RVOT by the artificial valved conduit in infants. The authors have been developing a mechanical mock circulatory system for the evaluation of RVOT reconstruction. Improving the inflow characteristics of the right ventricular function and pulmonary circulatory hemodynamics was essentially necessary for more precise evaluation of newly designed heart valves. We developed an original pediatric pulmonary mechanical circulatory system, which was capable of simulating normal pulmonary hemodynamics in children. The system consists of a pneumatic-driven silicone right ventricle, a pneumatic-driven right atrium with a bileaflet polymer valve, a pulmonary valve chamber with a visualization port, a pulmonary arterial compliance tubing, a pulmonary peripheral resistance unit, and a venous reservoir. The mechanical interaction between the right atrium and ventricle was pneumatically controlled by the originally developed microcomputer. Transvalvular pressure waveforms were measured by the pressure transducers and the pulmonary flow was obtained at the outflow portion of right ventricle by the electromagnetic blood flow probe. As a result, hemodynamic waveforms of either the right ventricle or atrium were obtained at the revised pulmonary mock circulatory system. The characteristics with atrial kick were well simulated as the natural hemodynamics. Moreover we could examine the effects of the bulging sinus structure on the valve leaflet motion in the vicinity of the leaflet as well as the atrial contraction. In this study, we simulated natural hemodynamics in our pulmonary circulatory system. We concluded that the simulation of right atrial contraction was inevitable in the quantitative examination of right heart prosthetic valves for congenital heart failure.