In brain ischemia, gating of postsynaptic glutamate receptors and other membrane channels triggers intracellular Ca²⁺ overload and cell death. In excitotoxic settings, the initial Ca²⁺ influx through glutamate receptors is followed by a second uncontrolled Ca²⁺ increase that leads to neuronal demise. Here we report that the major plasma membrane Ca²⁺ extruding system, the Na⁺/Ca²⁺ exchanger (NCX), is cleaved during brain ischemia and in neurons undergoing excitotoxicity. Inhibition of Ca²⁺-activated proteases (calpains) by overexpressing their endogenous inhibitor protein, calpastatin or the expression of an NCX isoform not cleaved by calpains, prevented Ca²⁺ overload and rescued neurons from excitotoxic death. Conversely, down-regulation of NCX by siRNA compromised neuronal Ca²⁺ handling, transforming the Ca²⁺ transient elicited by non-excitotoxic glutamate concentrations into a lethal Ca²⁺overload. Thus, proteolytic inactivation of NCX-driven neuronal Ca²⁺ extrusion is responsible for the delayed excitotoxic Ca²⁺ deregulation and neuronal death.