Cytosolic Ca2+ buffering determines the intra-SR Ca2+ concentration at which cardiac Ca2+ sparks terminate

- Cardiac Ca sparks terminate when [Ca]SR falls to a certain critical level.
- Local [Ca]SR depletion terminates a spark by reducing the unitary RyR current.
- The reduced RyR current decreases [Ca] around a RyR cluster, thus breaking CICR.
- Multiple CICR termination mechanisms co-exist to ensure a stability of Ca cycling.