Effect of initial conditions on steady-state behaviour. (a) Dynamic ion concentrations; (b) Dynamic intracellular ion concentrations; (c) Constant ion concentrations. The models were paced at 1 Hz for 30 min using a conservative stimulus current. [MgATP] = 6.95 mM, [MgADP] = 0.035 mM, [Pi] = 0.3971 mM, pH = 7.095, T = 310 K. Definitions: Vdia, diastolic membrane potential; APD, action potential duration at 90% repolarization. (Online version in colour.)