*isotropic dynamics* of the excitation vortex, that is with the fiber orientation data “turned OFF”, so that only the geometry of the otherwise isotropic homogeneous foetal heart affects the dynamics of the vortex. Here, again contrary to the expectation for a positive filament tension vortex to always contract, the organising filament first transiently extends intramurally before [breaking up]{} into the two ring-like pieces, each of which quickly contracts and terminates at the opposite base and apex regions of the heart, identical to what can be seen in the raw DT-MRI simulation shown in Fig. \[3D\_X\_iso\]. So that, this time, for this particular orientation of the initial re-entry, the “leftover” tissue “incidental capacitor” effect does not seem to play any role in the outcomes of the isotropic “heart geometry only” raw DT-MRI simulations shown in Fig. \[3D\_X\_iso\] as opoosed to the outcome of the identical initial re-entry location in the “edited” MRI simulations shown in Fig. \[3D\_X\_shaven\_iso\]. ]{}

Fig. \[3D\_X\_shaven\_aniso\] shows the *anisotropic dynamics* of the excitation vortex, that is with the fiber orientation data “turned ON”, so that both the anatomically realistic geometry and the anisotropy of the otherwise homogeneous foetal heart affect the dynamics of the initial vortex[, which, 