The main purpose of this study is to develop performance evaluation techniques that can evaluate the hydrodynamic characteristics of pediatric pulmonary heart valves. In this study, aperture ratios for artificial valves were evaluated using image processing. An ePTFE conduit with the bicuspid valve (14 mm) was fixed to a mock circulation system and was evaluated under hydrodynamic conditions found in pediatric pulmonary circulation (HR = 120 bpm, systolic ratio = 35 %, pulmonary artery pressure = 20-7 mmHg, flow rate = 700 mL/min). A biological valve (19 mm, Magna, Carpentier-Edwards) was used as a control valve. The valve leaflet movement was captured from the downstream side and the aperture ratios were calculated by image processing. As results, maximum aperture ratios of the bicuspid valve and the biological valve were 38.9±0.4 % and 31.6±0.7 %, respectively. This study suggested that it is possible to evaluate the performance of pediatric pulmonary heart valves using image processing.