The animation begins in an embryo at the beginning of the 21st day. The diagram shows the future pericardial cavity, cardiogenic plate, pericardioperitoneal canals and endocardial tubes. In the next sequence, the future pericardial cavity surrounds two endocardial tubes in an embryo at the end of the 21st day. The fusion of the endocardial tubes is animated in an approximately 22-day-old embryo along with the formation of the pericardial cavity, dorsal mesogastrium, and future transverse pericardial sinus. In the next sequence, the image is rotated toward the spectator and somewhat magnified. The diagram shows the pericardial cavity and the cardiac tube. In addition, the dorsal aortae and vitelloumbilical veins are shown. In the following sequence, the anterior part of the pericardial cavity and the entire cardiac tube are cut out and removed. On the diagram, the pericardium, pericardial cavity, sectioned truncus arteriosus and sinus venosus are visible. The two latter are incompletely surrounded by the pericardium. In addition, the dorsal mesocardium with the future transverse pericardial sinus are shown.

In an approximately 5-week-old embryo, the truncus arteriosus divides into the aorta and pulmonary trunk, while the sinus venosus shifts cranially and to the right. Here, the sinus venosus gradually forms the orifices of the future superior vena cava and the inferior vena cava. One left and one right pulmonary vein appear. The last sequence shows the formation of the right and left pulmonary veins in a pericardial reflexion. The latter separates the transverse pericardial sinus from the oblique pericardial sinus.

(This animation is essential for students of medicine and for departments of anatomy, histology, and embryology; it is also recommended for students of veterinary medicine, biology, and stomatology as well as for departments or clinics of pediatric and adult cardiology and cardiosurgery.)