Arrhythmias were simulated in sheets or cables, consisting of coupled excitable elements, which were characterized by a simple regenerative mechanism. The geometry of the network, the amount of coupling among individual elements, and the properties of the elements relating to excita-bility, automaticity, and duration of the refractory period could be adjusted arbitrarily in an interactive computer program. When a critical amount of coupling was present between automatic and non-automatic cells, sustained repetitive activity could be initiated and stopped by stimulation of the elements. Using this mechanism, it also was possible to evoke reciprocal activity in a one-dimensional cable. In uniform sheets of coupled elements, circus movement of the activation front could be evoked. The presence of an obstacle or dispersion of the refractory periods of the elements was not a prerequisite for the initiation of circus movements. The vortex of circus movements in the homogeneous sheets consisted of elements which were inactivated by depolarizing currents from the circulating wavefront. In sheets of sufficient size, multiple vortices could be present.Circ Res 47: 454-466, 1980