Abstract Body: Introduction: Signaling through the transcriptional co-activator Yes-associated protein (YAP) has been shown to protect the myocardium against ischemic or mechanical stress. Research Question: In light of the critical role of inflammation on adverse cardiac responses we examined the possibility that YAP regulates inflammatory responses to Angiotensin II (AngII)-mediated stress. Approach: Cardiomyocyte specific YAP-KO mice were generated, implanted with AngII minipumps, infused with AngII (1.5 mg/kg/min) or vehicle for periods of 3 hrs to 3 days and hearts collected for analysis. Results: YAP deletion markedly enhanced AngII-induced mRNA expression of pro-inflammatory cytokines and chemokines (e.g. CCL2, CXCL2, IL-6) at 3 or 24 hrs in the cardiomyocyte, but not non-myocyte cell fraction. Expression of mRNA for the hypertrophic genes ANP and MHC-β, in contrast, was decreased in YAP KO mice. After 3 days of AngII infusion there was enhanced mRNA for pro-fibrotic genes (Col1a1, Col3a1 and Periostin) and increased staining for COL1A1 and F4/80, indicative of increased fibrosis and inflammatory cell recruitment in the absence of YAP signaling. Single cell RNA sequencing revealed specific subsets of genes that were upregulated in the cardiomyocyte subcluster from YAP KO mice. These included pro-inflammatory cytokines, cJun family genes, TLR4 and, surprisingly, CaMKIId. Elevated activation of CaMKIIδ in response to AngII in YAP KO hearts was confirmed by increased phosphorylation of phospholamban. Cardiomyocytes expressing siYAP also showed enhanced expression of TLR4 and CaMKIIδ. Conclusion: Upregulated expression of cJun, TLR4 and CaMKII occurs in the absence of YAP and this conspires to create a greatly enhanced inflammatory milieu which fuels adverse responses to external insults. YAP activation serves to suppress these responses and thus temper development of maladaptive inflammation.