Figure 1

Folding of a sheet of heart tissue to make a spherical heart. An approximation of the orientation of muscle fibers in cardiac muscle may be obtained by considering a sheet of muscle wrapped to form a spherical chamber. In such an arrangement there is no single muscle fiber orientation. Rather, the fiber orientation changes with depth in the heart muscle. I assume fibers will point in all directions perpendicular to the chamber wall with depth and that this arrangement may be approximated as isotropic in the angular and azimuthal directions.