Does the right muscular atrioventricular valve in the avian heart perform two functions?

The right atrioventricular valve of adult birds is a muscular unicuspid structure and unlike the right atrioventricular valve in the adult mammalian heart. The aim of this study is to test the hypothesis that the avian muscular valve (MV) is a part of the cardiac wall during systole and contributes to the right ventricle pump function. Six adult hens Gallus gallus domesticus were examined with a focus on MV structure and function. The thickness of the right ventricle (RV) wall and MV were examined post-mortem. RV wall and MV end-systolic thickness were estimated echocardiographically. The frame-by-frame processing of RV images was applied for the analysis of MV and RV free wall motion. According to the post-mortem measurements, no significant difference in the thickness between RV free wall and MV (1.8±0.3 and 1.6±0.4 mm, respectively) was found. In the course of the entire cardiac cycle, MV demonstrated the excursion of 10.3±0.9 mm. To the end of RV systole, MV thickness was increased roughly by a factor of two (2.9±0.57 mm), and reached almost the same value (3.0±0.25 mm) in RV free wall. Based on the findings obtained, we concluded that the MV may play specific and non-specific roles in the avian heart. First, MV determines the blood flow separation between the right heart chambers. Second, MV performs contractility to support for RV pump function.