highlight the role and the necessity of the whole heart structure in the re-entry dynamics and self-termination.

[In the 3D DT-MRI based *isotropic* model of the foetal heart, depending on the initial location/orientation of the organising filament of the excitation vortex, the geometry of the foetal heart might sustain perpetual cardiac re-entry even with a positive filament tension, Fig. \[3D\_iso\]. However, if the same positive filament tension vortex is initiated at the exactly same location/orientation and in the same anatomical environment in the full *anisotropic* 3D DT-MRI based model of the heart, the realistic fiber structure of the foetal heart facilitates fast self-termination of cardiac re-entry, Fig. \[3D\_aniso\]. ]{}

[ From the respective comparison of the “isotropic vs anisotropic” simulations in FIG. \[3D\_iso\] vs FIG. \[3D\_aniso\], and FIG. \[3D\_shaven\_iso\] vs FIG. \[3D\_shaven\_aniso\], it can be seen that, whereas the re-entry filaments were capable to penetrate from the ventricles to atria in the isotropic simulations shown in FIG. \[3D\_iso\] and FIG. \[3D\_shaven\_iso\], the abrupt change in the fiber angles between the atria and the ventricles, which can be seen in FIG. \[HF\_slice\_x\_63\], did not allow the re-entry filaments to get from the ventricles to atria in the anisotropc simulations shown in 