EADs were produced by lowered g_K,s in Luo–Rudy cell models, and could be triggered by the addition of a small noise current. Endogenous EADs, produced in a fully deterministic, or a noise driven, one-dimensional virtual tissue could initiate ectopic (unidirectional or bidirectional) propagation, and retrograde, unidirectional propagation that is the analogue of reentry in a two-dimensional tissue. Such potentially reentrant activity occurred with a low probability, for a very narrow parameter range.