Simulated action potential and ionic currents at early embryonic stage with two different electrophysiological models. Simulated action potential can be divided into three phases: diastolic slow depolarization (DSD) phase, depolarization phase (DP), and repolarization phase (RP). (A) Simulated action potential, IKr current, and ICaL current in the Kyoto model. (B) Simulated action potential, IKr current, and ICaL current in the Luo–Rudy model. Sum of IKr and ICaL shows that the increase in outward (positive) current is slower in the Kyoto model than in the Luo–Rudy model