Communication between the SR (sarcoplasmic reticulum, SR) and mitochondria is important for cell survival andapoptosis. The SR supplies Ca2+ directly to mitochondria via inositol 1,4,5-trisphosphate receptors (IP3Rs) at closecontacts between the two organelles referred to as mitochondrion-associated ER membrane (MAM). Although it hasbeen demonstrated that CaR (calcium sensing receptor) activation is involved in intracellular calcium overload duringhypoxia/reoxygenation (H/Re), the role of CaR activation in the cardiomyocyte apoptotic pathway remains unclear. Wepostulated that CaR activation plays a role in the regulation of SR-mitochondrial inter-organelle Ca2+ signaling, causingapoptosis during H/Re. To investigate the above hypothesis, cultured cardiomyocytes were subjected to H/Re. Weexamined the distribution of IP3Rs in cardiomyocytes via immunofluorescence and Western blotting and found thattype 3 IP3Rs were located in the SR. [Ca2+]i, [Ca2+]m and [Ca2+]SR were determined using Fluo-4, x-rhod-1 and Fluo 5N,respectively, and the mitochondrial membrane potential was detected with JC-1 during reoxygenation using laserconfocal microscopy. We found that activation of CaR reduced [Ca2+]SR, increased [Ca2+]i and [Ca2+]m and decreased themitochondrial membrane potential during reoxygenation. We found that the activation of CaR caused the cleavage ofBAP31, thus generating the pro-apoptotic p20 fragment, which induced the release of cytochrome c frommitochondria and the translocation of bak/bax to mitochondria. Taken together, these results reveal that CaR activationcauses Ca2+ release from the SR into the mitochondria through IP3Rs and induces cardiomyocyte apoptosis duringhypoxia/reoxygenation.