FitzHugh-Nagumo model: rotating spirals, cardiac arrhythmias, Belousov-Zhabotinsky
The FitzHugh-Nagumo equations ∂u/∂t = D_u∇²u + u(1−u)(u−a) − v, ∂v/∂t = D_v∇²v + ε(u−βv) model excitable media. Spiral waves form when a broken wave front curls around a core region. In the heart, spiral waves (re-entry) underlie ventricular tachycardia; the Belousov-Zhabotinsky chemical reaction shows identical patterns due to universal excitable-medium dynamics.