Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): British Heart Foundation Background Cardiovascular issues associated with diabetes, such as diabetic cardiomyopathy (DCM), can lead to heart failure. DCM is etiologically related to myocardial inflammation and can stem from a complex interplay of different cell types. Cardiomyocyte as an active mediator of the inflammatory response is an emerging concept with limited mechanistic understanding. Purpose We aimed to address the knowledge gap of cardiomyocyte endoplasmic reticulum (ER) dysfunction-mediated macrophage response and provide functional evidence for the therapeutic feasibility of managing inflammatory paracrine signals in response to diet-induced metabolic stress. Methods In vivo mouse model of high fat high sucrose diet-induced diabetes, cardiomyocyte-specific p21-activated kinase 2 (PAK2) knockout model, echocardiography, histology, 3D imaging, qPCR, co-culture of H9c2 culturing medium and bone-marrow derived macrophages, immunoblotting, macrophage isolation from myocardium, flow cytometry and AAV9-gene therapy. Results In a time-course study, diet-induced diabetic mice demonstrated an association between cardiac ER stress and sustained myocardial inflammation, with a maladaptive shift in myocardial ER stress response over time. Furthermore, as a cardiac ER dysfunction model, mice with cardiac-specific PAK2 deletion exhibited heightened myocardial inflammatory response in diabetes. Using human and mice diabetic heart samples, we show that ER stress-induced CCAAT/enhancer-binding protein homologous protein (CHOP) is a novel transcriptional regulator of high mobility group box-1 (HMGB1). Cardiac stress-induced active release of HMGB1 facilitated M1 macrophage polarization, and aggravated myocardial inflammatory signatures. Therapeutically, sequestering the extracellular HMGB1 using Glycyrrhizin conferred cardioprotection through its anti-inflammatory action. Also, as functional evidence, we showed that un-mitigated cardiac ER response due to PAK2 loss under diabetes may account as a barrier for leveraging the anti-inflammatory potential of Vildagliptin. Conclusion Collectively, we introduce an ER stress-mediated cardiomyocyte-macrophage link, altering the macrophage response in the myocardium, thereby providing insight into therapeutic prospects for diabetes-associated cardiac dysfunction.