Proposed model for the role of Ca²⁺signaling in the commitment to becoming procoagulant. Platelet activators trigger an initial increase in [Ca²⁺]cyt that varies between platelets (1). This action will lead to variation in [Ca²⁺]mito (2), putting some above the threshold for mPTP opening. A supramaximal [Ca²⁺]cyt signal is triggered in these platelets (3), committing them to becoming procoagulant. Variation in the initial [Ca²⁺]cyt is therefore converted into 2 distinct subpopulations with distinct [Ca²⁺]cyt signals, leading to an all-or-nothing commitment to becoming procoagulant.