  We present systematic numerical studies of electrical-wave propagation in
two-dimensional (2D) and three-dimensional (3D) mathematical models, for human,
ventricular tissue with myocyte cells that are attached (a) regularly and (b)
randomly to distributed fibroblasts. In both these cases we show that there is
a parameter regime in which single rotating spiral- and scroll-wave states (RS)
retain their integrity and do not evolve to a state ST that displays
spatiotemporal chaos and turbulence. However, in another range of parameters,
we observe a transition from ST to RS states in both 2D or 3D domains and for
both cases (a) and (b). Our studies show that the ST-RS transition and rotation
period of a spiral or scroll wave in the RS state depends on (i) the coupling
strength between myocytes and fibroblasts and (ii) the number of fibroblasts
attached to myocytes. We conclude that myocyte-fibroblast coupling strength and
the number of fibroblasts are more important for the ST-RS transition than the
precise way in which fibroblasts are distributed over myocyte tissue.
