A resting cell fires if at least θ of its 8 neighbours are firing. A firing cell then steps through K−2 refractory states and back to rest. The seed sets K and θ, and the field starts from a few broken wave fragments.
Tap to fire a patch. The same ?seed= always gives the same run.
LITThe Greenberg–Hastings excitable medium (1978). Every step, the count in refractory state k must equal the previous count in state k−1, or the page throws.
WALLA cartoon of excitable tissue, not a cardiac model.