Altered regulation of signaling pathways can lead to pathologies including cardiac hypertrophy and heart failure. We report that neonatal and adult cardiomyocytes express chromogranin B (CGB), a Ca²⁺ binding protein that modulates Ca²⁺ release by the inositol 1,4,5-trisphosphate receptor (InsP₃R). Using fluorescent Ca²⁺ indicator dyes, we found that CGB regulates InsP₃-dependent Ca²⁺ release in response to angiotensin II, an octapeptide hormone that promotes cardiac hypertrophy. ELISA experiments and luciferase reporter assays identified angiotensin II as a potent inducer of brain natriuretic peptide (BNP), a hormone that recently emerged as an important biomarker in cardiovascular disease. CGB was found to regulate angiotensin II–stimulated and basal secretion, expression and promoter activity of BNP that depend on the InsP₃R. Moreover, we provide evidence that CGB acts via the transcription factor nuclear factor B in an InsP₃/Ca²⁺-dependent manner but independent of nuclear factor of activated T cells. In vivo experiments further showed that cardiac hypertrophy induced by angiotensin II, a condition characterized by increased ventricular BNP production, is associated with upregulation of ventricular CGB expression. Overexpression of CGB in cardiomyocytes, in turn, induced the BNP promoter. The evidence presented in this study identifies CGB as a novel regulator of cardiomyocyte InsP₃/Ca²⁺-dependent signaling, nuclear factor B activity, and BNP production.