The model parameters D=1, 
, 
, and 
were fixed to correspond to an excitable medium with a stable spatially
uniform steady state that can support stable rigidly rotating spiral waves
in the plane [25]. With the parameters chosen, the propagation
velocity of a solitary plane wave is approximately 1.8 su/tu, where su =
`space units' and tu = `time units'. The wavelength of the spiral wave is
36.4 su, with the core radius of 
su, and its period is about
21.4 tu. Since we are interested in re-entrant cardiac arrhythmia the size
of the circular domain, R=30, has been chosen of the same order as the
spiral wavelength. The hole radius was varied within 
. In
most of the computations the time step 
and both space and
angular steps 
, and 
were fixed. To
verify the robustness of the numerical results smaller time and space steps
and 
were sometimes used.