Fibrosis is a pronounced feature of heart disease and the result of dysregulated activation of resident cardiac fibroblasts (CFs). Recent work identified stress-induced degradation of the cytoskeletal protein βIV-spectrin as an important step in CF activation and cardiac fibrosis. Further, loss of βIV-spectrin was found to depend on Ca2+/calmodulin-dependent kinase II (CaMKII). Therefore, we sought to determine the mechanism for CaMKII-dependent regulation of βIV-spectrin and CF activity. Computational screening and mass spectrometry revealed a critical serine residue (S2250 in mouse, S2254 in human) in βIV-spectrin phosphorylated by CaMKII. Disruption of βIV-spectrin/CaMKII interaction or ablation of βIV-spectrin Ser2250 through alanine substitution (βIV-S2250A) prevented CaMKII-induced degradation, while a phospho-mimetic construct (βIV-S2254E) showed accelerated degradation in the absence of CaMKII. To assess the physiological significance of this phosphorylation event, we expressed exogenous βIV-S2254A and βIV-S2254E constructs in βIV-spectrin-deficient CFs, which have increased proliferation and fibrotic gene expression compared to wild-type (WT). βIV-S2254A but not βIV-S2254E normalized proliferation and gene expression. Pathophysiologic targeting of βIV-spectrin phosphorylation and subsequent degradation was identified in CFs activated with the profibrotic ligand angiotensin II (AngII), resulting in increased proliferation and STAT3 nuclear accumulation. While therapeutic delivery of exogenous WT βIV-spectrin partially reversed these trends, βIV-S2254A completely negated increased CF proliferation and STAT3 translocation. Moreover, we observed βIV-spectrin phosphorylation and associated loss in total protein within human heart failure (HF) tissue. Together, these data illustrates a considerable role for the βIV-spectrin/CaMKII interaction in activating profibrotic signaling.