The animation, intended for running on endless loop, shows how four variables Z, n, V and h of the model vary over the course of a control pace-making cycle. Z = cytosolic [Ca²⁺], n = gate state for IP₃R inactivation by Ca²⁺, V = membrane potential, and h = inactivation gate state for L-type calcium channels. Left: (Z,n)-space, showing the Z- and n‑nullclines. Right: (V,h)-space, showing the V- and h-nullclines.