Elastic fibers are crucial components of the vessel wall. They modulate the elasticity of arteries to enable a stable blood supply to peripheral organs. Vascular smooth muscle cells (VSMCs) are another major component of these vascular walls. Elastic fibers and VSMCs are arranged alternately to form a highly organized arterial media layer. VSMCs secrete several extracellular matrix components, such as tropoelastin, a precursor of elastic fibers. Elastic fibers, in turn, transmit several signals to determine the VSMC phenotype. Elastic fiber dysfunction, whether due to congenital anomalies or various arterial diseases, causes excessive accumulation of VSMCs and exacerbates disease progression, whereas physiological elastin deficiency and VSMC accumulation are essential for proper postnatal closure of the ductus arteriosus. In this review, we discuss elastic fiber formation and deficiency in the aorta and ductus arteriosus, and introduce recent insights into elastin deficiency-induced VSMC accumulation in these arteries.