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(Circulation Research. 2001;88:370.)
© 2001 American Heart Association, Inc.

Editorial

Getting to the Heart of Cardiac Morphogenesis

Margaret L. Kirby

From the Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, Ga.

Correspondence to Margaret L. Kirby, PhD, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30912-2640. E-mail mkirby@mail.mcg.edu

Key Words: atrioventricular junction • conduction system • atrioventricular node • heart development • vestibular spine

	Introduction

 
One of the most difficult concepts in heart development is to convert a looped tube with the presumptive right and left chambers in series to a 4-chambered heart with blood flowing from right atrium to right ventricle and left atrium to left ventricle. Try to explain how it happens to a room full of typical first-year medical students ("just tell me what I need to know") if you are into self-laceration.

The key to shifting from serially connected presumptive chambers to chambers connected in parallel is the atrioventricular (AV) canal. Because this little canal originally connects only the part of the tube that will become the atria with the part that becomes the left ventricle, it is critical that it moves or expands to gain access to the more distal part of the tube that will become the right ventricle. It is only possible because the tube is looped. It may be obvious that the myocardium at the inner part of the loop must be remodeled along with a change in position or expansion of the AV canal.

My awakening to the complexity of this region occurred several years ago with the publication of a study by Webb et al¹ in Circulation Research. Until then, my rather naive view of the AV canal was fairly simplistic and involved some shifting and fusion of the AV cushions. Webb et al presented a coherent exposition of the central mesenchymal mass (septum intermedium) in developing mouse embryos. This central mass comprises the . . . [Full Text of this Article]

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