The cytosolic Ca²⁺ concentration controls diverse cellular events via complex Ca²⁺ signalling patterns. Interactions between Ca²⁺ release channels on the sarcoplasmic reticulum (SR), and between the SR and other organelles such as mitochondria, establish the characteristics of the Ca²⁺ signal. Here, in single voltage-clamped guinea-pig colonic smooth muscle cells, IP₃-generating agonists evoked either repetitive Ca²⁺ oscillations or propagated waves. The forward movement of the Ca²⁺ wave arose from Ca²⁺-induced Ca²⁺ release (CICR) acting at the IP₃ receptor (IP₃R). IP₃-mediated Ca²⁺ waves are modulated by mitochondrial activity. Collapsing the mitochondrial membrane potential (necessary for mitochondrial Ca²⁺ uptake) inhibited Ca²⁺ oscillations and waves suggesting mitochondrial regulation of IP₃-mediated Ca²⁺ release itself. Indeed, preventing uptake of Ca²⁺ by mitochondria inhibited IP₃-mediated Ca²⁺ release. Mitochondria may accumulate Ca²⁺ to maintain a low local [Ca²⁺] near the IP₃R to prevent a Ca²⁺-dependent negative feedback on the receptor and so sustaining IP₃-mediated Ca²⁺ release. Mitochondria accomplished control of global IP₃-mediated Ca²⁺ rises by acting on the Ca²⁺ release events (‘puffs’) which arise from the activity of a single cluster of IP₃R; preventing mitochondrial Ca²⁺ uptake inhibited ‘puffs’. In this way mitochondria regulate local and global IP₃-mediated Ca²⁺ rises. To enable local control of IP₃-mediated Ca²⁺ release, mitochondria would be required to be largely immobile and potentially tethered. Indeed, in fully differentiated smooth muscle cells, mitochondria appear confined so that no displacement of the organelle was seen, either through trafficking or Brownian motion. Taken together, this data indicates that the positioning of mitochondria close to IP₃R clusters enables their control of local and global IP₃-mediated Ca²⁺ signals in smooth muscle.