The dynamics of phase disturbances in the 1D uniform medium
described by FitzHugh-Nagumo equations was studied. It was found that
the system synchronizes its oscillations of the initial disturbances are
small. Large disturbances resulted in the appearance of phase breaks.
Dependent on the system parameters, phase breaks were found to be either
stable or unstable; stable breaks led to target pattern - like sources,
unstable to extended chaos.