Fig. \[slice\_fig\], a counter-clockwise re-entry was initiated by the phase distribution method [@chaos], with the initial center of rotation placed at the prescribed location $x_0=40, y_0=60$ in the 2D cross section of the DT-MRI based anatomical model shown in Fig. \[HF\_slice\_x\_63\].

In the Fig. \[slice\_fig\](a-b), it can be seen that in both isotropic and anisotropic 2D simulations, at $t=0$, there was identical location of the initial re-entry rotation center: roughly in the middle of the slice, in the vicinity of the septum cuneiform opening.

Fig. \[slice\_fig\](a) shows the isotropic dynamics of the re-entry, that is with the fiber orientation data “turned OFF”, so that only the geometry of the isotropic homogeneous slice affects the dynamics of the re-entry. While it is known that in an infinite medium the chosen FHN kinetics parameter values ${\alpha}=0.3$, ${\beta}={0.71}$, ${\gamma}=0.5$ produce rigidly rotating spiral [@Winfree-1991], the anatomically realistic boundaries of the foetal heart cause the drift of the re-entry. The re-entry does not terminate because of the resonant reflection from the inexcitable boundaries [@Biktashev-Holden-1994], but after the transient first rotation around the septum cuneiform opening, the tip of the re-entry firmly pins to the sharp lower end of the cuneiform opening, see Fig. \[slice\_fig\](a).

