During exercise, local mechanisms in tissues cause arterioles to rapidly dilate to increase blood flow to tissues to meet the metabolic demands of contracting muscle. Despite decades of study, the mechanisms underlying this important aspect of blood flow control are still far from clear. We now report a novel mechanism wherein fibronectin fibrils in connective tissue matrices transduce signals from contracting skeletal muscle to local blood vessels to increase blood flow. Using intravital microscopy, we show that local vasodilation in response to skeletal muscle contraction is specifically inhibited by an antibody that recognizes the matricryptic site in the first type III repeat of fibronectin (FNIII-1). In the absence of skeletal muscle contraction, direct application of FNIII-1–containing fibronectin fragments to cremaster muscle arterioles in situ, triggered a rapid, specific, and reversible local dilation that was mediated by nitric oxide and required the cryptic, heparin-binding sequence of FNIII-1. Furthermore, application of function-blocking FNIII-1 peptides to cremaster muscle arterioles rapidly and specifically decreased their diameter, indicating that the matricryptic site of fibronectin also contributes to resting vascular tone. Alexa fluor 488–labeled fibronectin, administered intravenously, was rapidly assembled into elongated, branching fibrils in the extracellular matrix of intact cremaster muscle, demonstrating active polymerization of fibronectin in areas adjacent to blood vessels. Together, these data provide the first evidence that a matricryptic, heparin-binding site within fibronectin fibrils of adult connective tissue plays a dynamic role in regulating both vascular responses and vascular tone.