formed intramural laminar structure and more irregular epicardial, endocardial, and septal fibers, see Figure 4 of Pervolaraki et al [@Pervolaraki-etal-2013 p. 5] for the color-encoded fractional anisotropy (FA) and all the three components of the fiber angles in human foetal hearts. The DT-MRI based foetal heart model]{}]{} offered a unique opportunity to see if the 20 weeks of gestation age intramural heart structure was capable to support cardiac re-entry, as it would not be possible for the re-entry to pin to the endocardial fine features which were yet to be developed later, such as *e.g.* the pinning to pectinate muscles junction with crystae terminalis reported in adult human atria [@Wu-etal-1998-CR; @Yamazaki-etal-2012-CVR; @Kharche-etal-2015-BMRI]. ]{}

\[RD\] Cardiac Tissue Model
---------------------------

To investigate the effects of anatomy on cardiac re-entry dynamics we used *monodomain* tissue model with non-flux boundary conditions $$\begin{aligned}
 &
  {\frac{{\partial}{{{\mathbf{u}}}}}{{\partial}{\t}}} = \f ({{\mathbf{u}}})
  + \nabla\cdot\hat{{\mathbf{D}}}\nabla {{\mathbf{u}}},  
                \label{bc} \\ &
  \qquad \qquad {\normv \cdot\hat{{\mathbf{D}}}\nabla {{\mathbf{u}}}}\bigg|_G = 0,  
                \nonumber \end{aligned}$$ where ${{\mathbf{u}}}(\r,t)={(u, v)}^T$, $\r$ is the position vector, $\f(\r,t)={(f, g)}^T$ is the Fitz-Hugh-Nagumo [@Winfree-1991] kinetics column-vector $$\begin{aligned}
  f(u,v) &= {\alpha}^{-1}(u-u^3/3-v),                         \nonumber\\
  g(u,v) &= {\alpha}\, (  u + {\beta}- {\gamma}v ), \label{FHN}\end{aligned}$$ with the parameter values ${\alpha}=0.3$, ${\beta}={0.71}$, ${\gamma}=0.5$, which in an infinite 