AbstractBACKGROUND: Beluga (Huso huso) is one of the sturgeons and currently is cultured artificially in Iran with different goals. The cardiovascular system is one of the important systems of the body, and heart is the most important organ in this system. So far, few studies have been done on the heart of sturgeons.OBJECTIVES: This study was done to determine the exact structure of beluga different parts of the heart septum using echocardiographic and histologic techniques. METHODS: Six immature male belugas (2.5 years old) were investigated in this study. For echocardiography, probe was placed on the ventral surface of body, between pectoral fins. At first, macroscopic morphologic studies of different parts of heart were done at the topographic place of them. For histological studies, usual methods of fixation and hematoxylin and eosin (H&E) coloring were used. Prepared slides were studied by light microscope.RESULTS: All parts of the heart including the sinus venosus, atrium, ventricle, conus arteriosus and pericardium were clearly visible in different probe moves. The pericardium were covered surround heart`s structures having homogenous echo pattern. Sinus venosus had a very thin septum without any expansion and contraction. Atrium had a completed muscular septum with expansion and contraction. Ventricle muscular septum had two layers: an external compact layer and an internal spongy layer. Conus arteriosus was composed of obvious muscular septum and connective tissue. Histological studies showed three layers in beluga heart including epicardium, myocardium and endocardium. In overall, the histological findings were matched with the results of echocardiography. CONCLUSIONS: This study is the first investigation on echocardiographic feature of different parts of beluga heart. These results were coordinated with histological findings. Normal information and findings of this study can be used for investigation of various anatomic or pathologic changes in beluga heart in different research projects.