CFs are the main producers of core ECM proteins during cardiac development, and thus affect cardiomyocyte differentiation and maturation. During cardiac injury or chronic disease conditions, the ECM is altered, and fibroblasts interpret changes in mechanical tension and cytokine/chemokine signaling. They then differentiate to myofibroblasts that secrete the bulk of ECM proteins during adult cardiac wound repair and remodeling. This increased matrix deposition is sensed by cardiomyocytes, causing changes in cell phenotype such as hypertrophy. Abbreviations: GF, growth factors; ECM, extracellular matrix; TGFβ, transforming growth factor-β; IL-6, interleukin-6; PDGF, platelet derived growth factor.