The fast pacemaker (a = -0.1, ε = 0.03) and the slow one (a = -0.1, ε = 0.01) are placed on the plane with a = 0.1, ε = 0.032 to illustrate that fast pacemakers suppress slower pacemakers. Rectangular obstacle with a = 1, ε = 0.01 is added to the left. Boundaries are periodic.
You can make easy more complicated configurations. FHN systems are flexible and funny but there are more accurate heart tissue models e.g. Karma, BCF...