Calcium enters mitochondria through a dedicated channel referred to as the mitochondrial calcium uniporter (MCU), whose molecular identity has long remained elusive. Since the discovery of the gene encoding the MCU protein two years ago, researchers have awaited the generation of a mouse lacking the MCU. These mice are fully viable and show defects limited to performance of high-energy-demanding exercises. Strikingly, no protection against necrosis is observed following ischaemia-reperfusion in the heart.