This animation starts with the formation of the heart tube as viewed in mediosagittal section under low magnification for an approximately 17-day-old embryo. The cardiogenic area, splanchnopleuric and somatopleuric extraembryonic mesoderm are shown as well as numerous other details. The cardiogenic area is framed, cut out and magnified. The cardiogenic area is composed of pericardial celom and angiogenic cell clusters.

In the next sequence, an approximately 18-day-old embryo shows the formation of the pericardial celom (ancestor of the pericardial cavity), cardiogenic plate and a plexus of blood vessels. Then, an approximately 19-day-old embryo shows the cephalic folding of the embryo, which provokes the pericardial celom to rotate about 180 degrees. The cardiogenic plate and the pericardial cavity develop simultaneously along with the communicating channels between the endocardial tubes. The animation continues with an approximately 20-day-old embryo to show the further evolution of the endocardial tube, myocardial mantle (former cardiogenic plate) and pericardial cavity.

At the same time, cardiac jelly, umbilical and vitelline veins and horns of the sinus venosus develop. In an approximately 21-day-old embryo, the myocardial mantle surrounds the endocardial tubes, and the dorsal myocardium develops. In an approximately 22-day-old embryo, the endocardial tube becomes cardiac tube with the following dilatations: truncus arteriosus, bulbus cordis, primitive ventricle, common atrium and sinus venosus.

The early phase of the heart development is then viewed from the amniotic cavity. The starting diagram shows an approximately 16-day-old presomite embryo. The appearance of the celomic vesicles is observed by transparence in an approximately 17-day-old embryo. In an approximately 18-day-old embryo, the celomic vesicle fuse to form a horseshoe-shaped celomic space composed of a pericardial celom and a celomic canal. In the next sequence, the extension of the celomic canal is indicated by arrows. In an approximately 20-day-old embryo, the cardiogenic area, cardiogenic cords and pericardial celom develop. In the next sequence, the outlines of the amnion and the yolk sac are removed to show the anteroposterior flexion of the embryo, i.e. rotation of the cardiogenic area.

Parallel to the rotation of the cardiogenic plate, two endothelial (endocardial) tubes are interconnected by a vascular plexus. The endocardial tubes and myocardial mantle further evolve in an approximately 21-day-old embryo. The dorsal aortae and vitelloumbilical vein also appear. The endocardial tubes fuse due to the lateral folding of the embryo. Different portions of the endocardial tubes are indicated. In an approximately 22-day-old embryo, two endocardial tubes fuse into the cardiac tube, which is surrounded by the myocardium.

The next sequence shows the formation of the cardiac tube as viewed in section under high magnification. For this purpose, an approximately 18-day-old embryo is cut just in front of the buccopharyngeal membrane; this section is cut out and magnified. The starting diagram depicts the layers of the embryonic disc, indicating among other structures the intraembryonic mesoderm, cardiogenic plate, angiogenic clusters and celomic canal. From the 18th to the 21st day, the two endocardial tubes form by fusion of angiogenic cells clusters and move close to one another. Through this movement, the foregut becomes separated from the yolk sac. The next sequence animates the fusion of the two endocardial tubes in a cardiac tube composed of the endocardium, cardiac jelly, myocardial mantle and epicardium. In the dorsal mesocardium, a localized degeneration develops, which will later form the sinus transversus pericardii. All of the mentioned structures are located within the pericardial cavity.

In order to summarize the early development of the heart, the formation of the endocardial tubes is animated in 3D.

For this purpose, an approximately 17-day-old embryo is shown in semiprofile in 3D. Primitive node, primitive streak, ectoderm, endoderm, extraembryonic mesoderm and allantois are represented. Then, the embryo is cut transversally and removed excepting the endoderm. The diagram is arranged in this manner to permit observation of all embryonic layers. First, the celomic vesicles form by fusion the celomic canals in an approximately 19-day-old-embryo. Among numerous other details, the pericardial celom, cardiogenic area, cardiogenic cord and angiogenic clusters are shown.

The next sequence shows the longitudinal and lateral folding of the embryo between the 19th and 21st day. The pericardial cavity and the pericardioperitoneal canals rotate, and two endocardial tubes form. The future dorsal aortae, vitelloumbilical veins, stomodeum, buccopharyngeal membrane, foregut, midgut, somites and neural tube are shown.

The next sequence illustrates the formation of the endocardial tubes as viewed under high magnification. An approximately 19-day-old embryo is shown in semiprofile in 3D. Two parallel paramedial sections are made through the pericardial celom, cardiogenic area, and adjacent cardiogenic cords. The plexus of small blood vessels, pericardial celom and cardiogenic plate are magnified. In the next sequence, two endocardial tubes form from the plexus of small blood vessels in an approximately 20-day-old embryo. Because of the cephalocaudal folding and lateral folding of the embryo during the 21st day, the endocardial tubes, pericardial cavity and cardiogenic area rotate approximately 180 degrees. The endocardial tubes are pushed into the pericardial cavity, and the pericardioperitoneal canals approach one another. In an approximately 22-day-old embryo, the endocardial tubes fuse to form a cardiac tube. The parts of the cardiac tube, sinus venosus, dorsal aortae, vitelline and umbilical veins are described. In addition, the outline of the pericardial cavity and the future sinus transversus pericardia are shown.

The next sequence shows the formation of the cardiac tube, pericardial cavity and the dorsal mesocardium as viewed in profile and in 3D during the course of the 21st day. For this purpose, the endocardial tubes, future pericardial cavity, dorsal aortae and vitelloumbilical veins are cut vertically. All superfluous structures are removed to be concentrate on the evolution of the endocardial tubes as viewed under high magnification. The first diagram shows the sectioned endocardial tubes, each of which is flanked by cardiogenic plates and partially surrounded by the future pericardial cavity. The image is magnified and rotated to show the endocardial tubes from above. Thus, the final diagram of this sequence shows the two endocardial tubes with their communicating channels, cardiac jelly, myocardial mantle, and pericardial folds of the future pericardial cavity. The next sequence demonstrates the fusion of the endocardial tubes and the formation of the dorsal mesocardium in an approximately 22-day-old embryo. A single cardiac tube forms within the pericardial cavity. The pericardial folds fuse to form the dorsal mesocardium. In addition, the rupture in the distal mesocardium is also shown.

To follow the development of the cardiac tube, the dorsal aortae and vitelloumbilical veins are removed, and the pericardial cavity is shown. The obtained image is rotated in the vertical position. The final diagram of an approximately 22-day-old embryo shows the pericardial cavity, from which emerge the dorsal aortae, primitive atria and horns of the sinus venosus.

To show the structure and function of the cardiac tube, the pericardial cavity and cardiac tube are cut longitudinally. The obtained diagram details the subdivision of the cardiac tube and its histological stratification in a 22-day-old embryo. Then, the next sequence animates the pumping contractions of the newly formed cardiac tube.

The next sequence addresses the formation of the cardiac loop.

The first diagram shows the frontal view of the cardiac tube within the pericardiac cavity. Projections of the interventricular and atrioventricular junctions are marked. From the 22nd to 23rd day, the cardiac tube bends into the cardiac loop. The aortic arches, truncus arteriosus, bulbus cordis, primitive ventricle, common atrium, sinus venosus, common cardinal veins, vitelline and umbilical veins develop. Simultaneously, the projections of the primary interventricular foramen and the atrioventricular canal move. In an approximately 30-day-old embryo, the common atrium ascends and divides into the right and left atrium. In addition, the common ventricle subdivides into the primitive right and left ventricles. The bulbus cordis, 3rd, 4th, and 6th aortic arches also form.

The next sequence animates the transformation of the cardiac tube into the cardiac loop as viewed from profile from the left. For this purpose, the cardiac tube of an approximately 22-day-old embryo rotates 90 degrees. The truncus arteriosus, bulbus cordis primitive ventricle, common atrium and horns of the sinus venosus form. The displacement of the projection of the primary interventricular foramen and the projection of the atrioventricular canal are also animated. In an approximately 23-day-old embryo, the common atrium, sinus venosus and atrioventricular canal continue to ascend behind the bulbus cordis and primitive ventricles. In an approximately 30-day-old embryo, the common atrium subdivides into the primitive right and left atrium, and the sinus venosus are situated dorsocranially from the bulbus cordis and primitive ventricles. The shift of the projections of the primary interventricular foramen and the atrioventricular canal are also animated. The final diagram contains more than 15 legends.

The next sequence shows the transformation of the cardiac tube into the cardiac loop viewed from the dorsal side.

The cardiac tube of an approximately 22-day-old embryo rotates 90 degrees. The next sequence shows the ascent of the sinus venosus and the common atrium behind the bulbus cordis. The projections of the atrioventricular junction and the sinuatrial junction shift. (In order to simplify the diagram, the moving of the primary interventricular foramen is not shown.) The next sequence shows an approximately 23-day-old embryo. The common atrium and the now-single sinus venosus climb the dorsocranial. The sinuatrial junction and atrioventricular canal shift.

In an approximately 27-day-old embryo, the common atrium and sinus venosus continue their dorsocranial ascent. The common atrium and primitive ventricle simultaneously divide.

In an approximately 30-day-old embryo, the atria are situated behind the truncus arteriosus. This animation shows the obliteration of the left umbilical and vitelline veins as well as the main part of the left common cardinal vein. The formation of the oblique vein of the left atrium is also animated. In addition, the venae cavae and future coronary sinus form during this sequence. Among other details, the displacements of the atrioventricular canal and the sinuatrial orifice are shown.

The next sequence shows the anterior view of the early evolution of the cardiac cavities starting in an approximately 22-day-old embryo. The pericardium, pericardial cavity and frames symbolizing the cardiac jelly and myocardium are shown.

The cardiac tube faces the spectator. Then, the cardiac tube bends to form the cardiac loop. The bulbus cordis, primitive right and left ventricles, bulboventricular sulcus, bulbo(cono) ventricular flange and interventricular sulcus are shown. In an approximately 30-day-old embryo, the sinuatrial orifice, atrioventricular canal and primary interventricular foramen shift.

This animation concludes with malformations, including acardia, ectopia cordis and dextrocardia.

The development of the sinus venosus starts with an approximately 30-day-old embryo and ends with an 8-week-old fetus. The incorporation of the right sinus horn (superior and inferior venae cavae) into the right atrium and the further transformation of the left sinus horn into the definitive oblique vein of the left atrium and the definitive coronary sinus are animated. The aorta arch and branches, pulmonary veins, ductus arteriosus, pulmonary arteries develop. The derivatives of the former right and left sinus horns are numbered.

To animate the septum formation in the common atrium, the heart of an approximately 28-day-old embryo is cut vertically through the common atrium and common ventricle and then rotated to the left. Besides the common atrium and ventricle, the sinuatrial orifice delimited by the right and left sinus valves, septum spurium, common pulmonary vein, and right and left endocardial cushions are visible. An approximately 33-day-old embryo shows the development of the sinus venarum, septum primum, interventricular septum, ostium (foramen) primum and inferior endocardial cushion. In an approximately 38-day-old embryo, the ostium primum closes, and the septum and ostium secundum appear. Through the interventricular foramen, the vetricles communicate, and new pulmonary veins open into the left atrium.

The following animation covers the end of the 7th week. The ostium secundum appears in the septum primum and the foramen ovale in the septum secundum. The endocardial cushions fuse, and the primordia of the tricuspis and mitral valves appear. The closure of the intervetricular septum is also animated.

To show the above-described events more clearly, the septum formation in the common atrium is viewed from the right.

The sequence begins with an approximately 28-day-old embryo, illustrated by a sagittal section of the primitive right atrium, conus cordis and primitive right ventricle. The image is rotated to show the common atrium and common ventricle. The diagram reveals the inferior and superior endocardial cushions, future atrioventricular canal, sinuatrial orifice, septum spurium, and superior and inferior venae cavae, among other details.

In an approximately 30-day-old embryo, the septum primum and interventricular septum grow along with the inferior and superior endocardial cushions, ostium primum and interventricular foramen.

The next sequence shows the near-complete separation of the atria from the ventricles as well as the formation of the ostium secundum in an approximately 32-day-old embryo. An approximately 33-day-old embryo and an embryo at the end of the 7th week depict the closure of both the ostium primum and the interventricular foramen as well as the formation of the septum secundum. In addition, the incorporation of the sinus venosus into the right ventricle and the appearance of the crista terminalis are shown. The last diagram shows the ostium secundum covered by the septum secundum, the foramen ovale and the future valve of the foramen ovale.

Two diagrams simultaneous depict the fetal blood circulation between the two atria after the formation of the foramen ovale. Both show the heart of embryos at the end of the 7th week: one diagram is a frontal section of the heart, while the other is a sagittal section. In both diagrams, thick arrows symbolize bloodstreams. From the inferior vena cava, the bloodstreams are directed toward the foramen ovale and the left atrium. Only a small amount of blood is separated by the crista dividens and remains within the right atrium.

Malformations, animated as atrial septal defects (ADSs) in the frontal view, include the complete absence of the atrial septum, the absence or inadequate development of the septum secundum, excessive death and resorption of the septum primum, premature closure of the oval foramen, ostium primum defect and persistent atrioventricular canal.

The next sequences are dedicated to the formation of the aorticopulmonary septum, the conus septum and the interventricular septum.

For this purpose, the heart of an approximately 28-day-old embryo is rotated to the left and magnified. Then, the truncus aortic arches are cut out and removed. A vertical section reveals the primitive right and left ventricles as well as the atrioventricular canal. An approximately 30-day-old embryo shows the migration of the atrioventricular canal and the appearance of the bulbo(cono)ventricular flange and primordium of the interventricular septum. The outline of the truncus arteriosus is indicated. In an approximately 32-day-old embryo, the bulbo(cono)ventricular flange moves toward the superior atriventricular endocardial cushion, while the interventricular septum moves toward the inferior atrioventricular endocardial cushion. The lateral atrioventricular endocardial cushion also appears. The same diagram illustrates the developing neural tube and groups of neural crest cells. In the next sequence, the neural crest cells migrate from the myelencephalon and contribute to the formation of the right and left conotruncal swellings or ridges.

In an embryo during the course of the 6th week the fusion of the contralateral conotruncal ridges and the formation of the aorticopulmonary or contruncal is shown. The helicoidal growth of the aorticopulmonary septum toward the primitive ventricle is animated. The superior and inferior atrioventricular endothelial cushions fuse to form the right and left atrioventricular orifices. The growth of the interventricular septum toward the fused cushions then ceases, and the primordia of the aortic and pulmonary semilunar valves appear in the conotruncus.

In an embryo at the beginning of the 7th week, the helicoidal growth of the aorticopulmonary septum continues, but it does not fuse with the interventricular septum, leaving the interventricular foramen. At the same time, the right atrioventricular orifice transforms into the tricuspid orifice and the left atrioventricular orifice into the mitral orifie. The papillary muscles appear in the primitive right ventricle. (Because the chronology of developmental events is argued in the literature, approximately one week can be added to the indicated times).

In this stage, two outflow channels, the aortic and the pulmonary, develop. Because of the helicoidal course of the aorticopulmonary and conus septum, the bloodstreams circulating within the both outflow channels twist around each other.

The next sequences animate two theories concerning the closure of the interventricular foramen, starting from the beginning of the 7th week. The first theory argues that the interventricular foramen closes by outgrowing the inferior atrioventricular endocardial cushion along the edge of the muscular part of the interventricular septum. The second theory states that the continuation of the aorticopulmonary septum, the conus septum, fuses with the muscular part of the interventricular septum at the end of the 7th week.

The next sequence demonstrates the separation of the pulmonary trunk from the aorta as a consequence of the cranial growth of the aorticopulmonary septum. The sequence starts with an approximately 32-day-old embryo and ends with an approximately 8-week-old fetus. The cranial growth of the conotruncal ridges is animated in parallel with the helicoidal caudal growth of the aorticoplumonary septum. The rotation of this septum is viewed from above. At the same time, the individualization and clockwise rotation of the pulmonary trunk and aorta are shown. The common ventricle separates from the conus septum. Finally, the heart is closed, and normal anatomy is established.

Malformations of the closure of the interventricular foramen include ventricular septal defects (VSDs) such as the tetralogy of Fallot, persistent truncus arteriosus and transposition of great vessels. This sequence begins with normal development for comparison. In some cases, blood circulation in the malformed heart is animated.

The next sequence shows the formation of the semilunar valves. For this purpose, a segment of the truncus arteriosus of an approximately 30-day-old embryo is cut out, moved to the center of the screen and magnified.

A 5-week-old embryo shows the cranial growth of the aorticopulmonary septum and the formation of small swellings on the left and right truncus ridges. The ridges approach one another during the course of the 6th week. At the same time, small excavations appear in these ridges, and anterior and posterior tubercles develop. In a 7-week-old embryo, the right and left truncus ridges fuse, and the truncus arteriosus divides into the pulmonary and aortic channels. Excavations into the mesenchymal tissue of the tubercles continue. The animation shows the separation of the pulmonary and aortic channels in an 8-week-old fetus. The structure of the newly formed aortic and pulmonary semilunar valves is described.

In order to show the formation of the semilunar valve cusps within the aortic/pulmonary channel, a segment of an embryo at the end of the 5th week is placed in the centre of the screen, cut vertically and opened. At the beginning of the 6th week, small mesenchymal tubercles appear on opposite sides. Parallel with the growth of the tubercles, they form mesenchymal cavities in an approximately 7-week-old embryo. Finally, in an approximately 8-week-old embryo, the excavations transform into sinuses and the thinned mesenchymal tissue into cusps of the semilunar valves.

The next sequence presents an external view of the separation of the ascending aorta from the pulmonary trunk.

The diagram shows the heart of an approximately 30-day-old embryo, whose truncus arteriosus is divided into the pulmonary trunk and the aorta ascendens according to the same mechanism animated for the formation of the semilunar valves.

The following malformations of the semilunar valves are animated: valvular stenosis of the pulmonary trunk, pulmonary valvular atresia, aortic valvular stenosis and aortic valvular atresia. In some of these malformations, blood circulation is also shown.

In order to summarize the animated events, special sequences provide an anterior view of the formation of the pulmonary semilunar valve, atrioventricular valves, aorticopulmonary septum and the partition of atrioventricular canal.

The first diagram describes the heart of an approximately 28-day-old embryo. The heart is sectioned in the frontal plane, opened, and described. The bulbus cordis, primitive atria and ventricles, atrioventricular canal, primary interventricular foramen, interventricular septum and bulbo(cono)ventricular flange are shown. From the 28th to the 32nd day, the right and left conotruncal swellings and four atrioventricular endocardial cushions appear. During the course of the 6th week, the inferior and superior atrioventricular endocardial cushions fuse to form the septum intermedium. The conotruncal swellings form the aorticopulmonary (conus) septum and provide material for the pulmonary semilunar valves. At the same time, the papillary muscles start to develop. Through the end of the 7th week, the helicoidal growth of the aorticopulmonary (conus) septum is detailed along with the evolution of the pulmonary semilunar valve and papillary muscles. The origin of cusps of the tricuspidal and mitral valvulae from atrioventricular endocardial cushions is also demonstrated.

As malformations of the aorticopulmonary septum, the persistent atrioventricular canal and the tricuspid atresia are compared with the normal heart. In the latter anomaly, blood circulation is also shown.

The next sequence is dedicated to the outflow channels of the heart in an embryo at the end of the 7th week. The direction of the venous blood from the right atrium to the right ventricle and pulmonary trunk is indicated by a thick arrow. The circulation of oxygenated blood from the left atrium to the left ventricle and into the ascending aorta is indicated in the same manner.

In order to show the formation of the atrioventricular valves, papillary muscles and cordae tendineae, the heart of an approximately 36-day-old embryo is opened and cut obliquely through the inferior and lateral atrioventricular endocardial cushions of the atrioventricular canal. This image is rotated toward the spectator and magnified. The right, left, and inferior atrioventricular cushions, primitive right and left ventricles and interventricular septum is framed and magnified. From an approximately 36-day-old embryo to an approximately 8-week-old fetus, the process of carving papillary muscles in both ventricles is animated. In addition, myocardial strands are replaced by dense connective tissue to form the chodae tendineae. Simultaneously, the endocardial cushions gradually transform into the dense connective tissue of the future cusps of the tricuspid and the bicuspid valves.

An 8-week-old fetus and an approximately 3-month-old fetus show the definitive forms of the papillary muscles, chordae tendineae and atrioventricular cusps.

The formation of the impulse-conducting system (pacemaker tissue) of the heart begins with an approximately 33-day-old embryo, illustrating the future sinuatrial node. The internodal atrial pathway, where the atrioventricular node will develop, grows from the sinuatrial node. The atrioventricular bundle grows from the atrioventricular node, and its Purkinje's fibres begin to ramify within the myocardium. The last sequence depicts the morphology and components of the impulse-conducting system for an approximately 3-month-old fetus.

The animation concerning the development of the heart continues with the animated chapter demonstrating the blood circulation through the embryonic and fetal heart (2101).

The following phases of blood circulation are animated: plexiform phase (21st day), loop phase (23th day), the in series heart (24th day), the in parallel heart (25th day), and the in parallel heart during the formation of the septum in the atrioventricular canal and fetal stage.

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