Perturbing CRU positions around their original square lattice positions increases synchronization and recruitment of CRU to release Ca via locally propagating CICR, resulting in earlier activation of I _NCX and shorter AP firing cycle. (A–D) Shown are representative examples of simulations of V_m (A), number of open CRUs at a given time (B), I_NCX (C), and I_CaL (D). The traces are synchronized at the MDP to clearly see difference in time course during diastolic depolarization.