1. Cardiac Septation UNSW Embryology Heart - day 40 (ventral view)

2. primordial right atrium primordial left atrium primordial left ventricle primordial right ventricle fused endocardial cushions sinus venosus opening Heart - day 40 (ventral view) Dorsal and ventral endocardial cushions fuse, generating left and right channels

3. primordial right atrium primordial left atrium primordial left ventricle primordial right ventricle fused endocardial cushions sinus venosus opening Heart - day 40 (ventral view) Dorsal and ventral endocardial cushions fuse, generating left and right channels

4. Septum primum - myocardium differentiated from splanchnic mesenchyme near the venous pole septum primum

5. Septum primum grows downward towards fused endocardial cushions

7. septum primum foramen primum Septum primum growth Septum primum growth generates foramen primum

8. septum primum foramen primum Septum primum growth Septum primum growth generates foramen primum

9. septum primum foramen primum Septum primum growth Septum primum - myocardium differentiated from splanchnic mesenchyme near the venous pole

10. septum primum foramen primum Septum primum growth

12. Septum primum perforation begins to degenerate to form opening Septum primum perforation begins to degenerate to form opening

13. Ventricular septum growth

14. sinus venosus valve pulmonary veins opening ventricular septum Septum primum perforates and the ventricular septum begins growth Septum primum perforates and the ventricular septum begins growth

15. sinus venosus valve pulmonary veins opening ventricular septum Septum primum now perforates and the ventricular septum begins growth Septum primum now perforates and the ventricular septum begins growth

16. Ventricular septum growth ventricular Septum Ventricular septum growth Early studies thought that the ventricular septum formed from coalescence of trabeculae of the primordial ventricle Ventricular septum growth Early studies thought that the ventricular septum formed from coalescence of trabeculae of the primordial ventricle

17. Ventricular septum growth ventricular Septum Ventricular septum growth Early studies thought that the ventricular septum formed from coalescence of trabeculae of the primordial ventricle Ventricular septum growth Early studies thought that the ventricular septum formed from coalescence of trabeculae of the primordial ventricle

18. ventricular septum

19. Ventricular septum Ventricular septum growth Later studies show the muscular septum arises from fusion of the external R and L ventricular walls with ventricular growth Ventricular septum growth Later studies show the muscular septum arises from fusion of the external R and L ventricular walls with ventricular growth

20. Ventricular septum Ventricular septum growth Later studies show the muscular septum arises from fusion of the external R and L ventricular walls with ventricular growth Ventricular septum growth Later studies show the muscular septum arises from fusion of the external R and L ventricular walls with ventricular growth

22. Septum secundum growth

23. Ventricular trabeculation

24. Septum secundum growth septum secundum foramen secundum foramen ovale

25. Septum Secundum forms as a superior interarterial fold septum secundum

26. Septum Secundum forms as a superior interarterial fold septum secundum

28. Septum Secundum Septum secundum also from the original cardiogenic fields left sided mesenchyme

29. Septum Secundum Septum secundum also from the original cardiogenic fields left sided mesenchyme

30. Ventricular Trabeculation…something about this process

32. trabeculae