Cardiovascular disease (CVD) is a leading cause of death worldwide. We previously reported that the Sigma-1 receptor (Sigmar1) is down-regulated in mice with cardiac dysfunction. Recent study suggested that Sigmar1 deficient mice display cardiac dysfunction via impairment of mitochondrial function. However, the mechanism of mitochondrial quality control mediated by Sigmar1 has not been investigated in detail. In this study, we investigated the role of Sigmar1 for ER-mitochondrial tethering and mitochondrial Ca²⁺ signaling using a Sigmar1-knockdown cardiomyocytes. We found that disruption of ER-mitochondrial tethering and reduction of ER-mitochondrial Ca²⁺ transport was induced by Sigmar1 knockdown in cardiomyocytes. We also demonstrated that Endothelin-1-induced cardiomyocyte hypertrophy is aggravated associated with induction of mitophagy in Sigmar1 knockdown cardiomyocytes. These data suggest that reduction of cardiac Sigmar1 is involved in myocyte hypertrophy by maintaining of intracellular Ca²⁺ signaling mediated by regulation of ER-mitochondrial tethering.