The human heart actively releases protein messengers into the extracellular space. Recent work suggests that these secreted proteins, termed cardiokines, can mediate cellular crosstalk that plays important roles in the development of cardiomyopathies and heart failure. Although several classical cardiokines such as the natriuretic peptides have been extensively characterized, there have been few efforts to systematically catalog the proteins secreted by human cardiac cells. Using proteomics and human induced pluripotent stem cell (hiPSC) models, we recently created a draft map of the human cardiac secretome through identifying and contrasting secreted molecules from hiPSC-derived cardiomyocytes, cardiac fibroblasts, and endothelial cells. The results revealed a surprisingly large number of candidate cardiokines released from each cell type including many secreted proteins with uncharacterized function in the cardiovascular system. Moreover, we found broad changes in the secretome patterns of cardiomyocytes carrying dilated cardiomyopathy causal variants over normal cells. Building on these findings, our aims in the R00 phase are now to (i): identify cardiomyocyte secreted proteins that function in fibroblast crosstalk and predict the biological processes they regulate; and (ii) prioritize disease-relevant cardiokines and validate their effects on recipient fibroblast gene expression. To achieve these aims, we will employ a combination of computational, single-cell sequencing, and proteomics strategies building on hiPSC models as our foundation. If successful, the proposed research has the potential to uncover a number of novel secreted proteins and their function in human cardiac cells, and shed light on the role of cellular communications in the development and progression of cardiomyopathies.