the septum opening in the isotropic simulation in Fig. \[slice\_fig\](a), or to the whole septum opening as an anatomical re-entry in the anisotropic simulation in Fig. \[slice\_fig\](b), despite of the only basic segmentation of the MRI model into the tissue/not tissue points, and the ventricles not being isolated from the atria, the tip of the re-entry never got from the ventricles into the atria, Fig. \[slice\_fig\]. ]{} [Although, from the cardiac physiology point of view, the [[ [ only basic segmentation of the raw DT-MRI data [@Pervolaraki-etal-2013] into the tissue/non-tissue pixels]{} might be seen as]{}]{} a major limitation of the study, from the non-linear science point of view, the use of the raw MRI data as an example of a nature provided medium to study a re-entry dynamics gives an important insight into the pure anatomy induced drift in an otherwise homogeneous 2D medium, and into the possibility of pinning of the re-entry not to a major blood vessel but to a sharp end of an anatomical openning [@Biktasheva-etal-2015-PRL]; and into that a real fiber anisotropy is capable to turn the pinned re-entry into an anatomical one.]{} Importantly though, the 2D simulations in Fig. \[slice\_fig\] are an important step to 