Cardiac fibroblasts are generally considered the primary cell type that controls extracellular matrix homeostasis in the heart. Distinct changes in amounts and composition of extracellular matrix occur from birth to old age. Accordingly, age-dependent alterations in cardiac extracellular matrix are an important factor governing response to injury and pathological remodeling. Whereas cardiac myocytes are surrounded by a basal lamina, cardiac fibroblasts do not assemble a cell-adjacent basal lamina. Evidence is presented that in addition to fibrillar collagen production, cardiac fibroblasts are also the primary cell type responsible for the production of collagen IV. First, patterns and abundance of collagen IV in murine heart was established in sections from neonate, adult, and aged mice. Second, production of collagen IV by fibroblasts grown in 3-D fibrin gels was assessed by confocal microscopy and quantification by immmunoblot analysis. Finally, co-cultures of cardiac fibroblasts with myocytes were performed to show that fibroblasts are the primary cell type producing collagen IV under these conditions. The basal lamina of the myocytes plays a critical role in aligning and tethering myocytes together as well as making connections to the interstitial collagen fibers of the heart. Hence, production of collagen IV by cardiac fibroblasts would provide a mechanism by which cardiac fibroblasts assist in aligning and securing cardiac myocyte alignment and structural integrity via basal lamina production.