Determinants of heart shape in early embryos.

The early embryonic vertebrate heart is a tubular organ that changes shape rapidly. It acquires a pronounced bulge, and bends and rotates to the right side in a process called looping. There has been to date no satisfactory explanation of the mechanisms regulating this morphogenetic sequence. Evidence is presented suggesting that this is a physical deformation rather than the result of differential growth. The control of heat deformation is discussed and possible regulatory mechanisms are explored. It is not yet possible to identify all the factors responsible but it appears that a number of independently regulated variables such as cytodifferentiation and matrix production interact to regulate expression of complex shapes.