BACKGROUND:: Heart health benefits have been attributed to regular consumption of oats. Preclinical evidence suggests that a wild green oat extract (WGOE) may improve vasodilator function, but this is yet to be evaluated in humans. OBJECTIVE:: To determine whether regular daily consumption of WGOE can influence vasodilator function in systemic and cerebral arteries. METHODS:: Thirty-seven healthy older adults (>60 years) completed a 24-week randomized, double-blind, placebo-controlled two-way crossover dietary intervention with 1500 mg/day of encapsulated WGOE or placebo. All assessments were conducted at the end of each 12-week intervention arm, after participants had fasted for at least 4 h and at least 18 h after they had taken their last dose of supplement. Flow-mediated dilatation (FMD) of the brachial artery and hypercapnia-induced increases of blood flow in the middle cerebral artery were used to measure systemic and cerebral vasodilator responsiveness (CVR), respectively. RESULTS:: Compared with placebo, WGOE supplementation increased CVR and FMD to a similar extent (42 and 41%, respectively, P < 0.01 for both). The improvements in CVR and FMD were not correlated. Resting blood pressure did not alter with supplementation. Dose and treatment duration were well tolerated by participants. CONCLUSION:: WGOE supplementation can improve vasodilator function in systemic and cerebral arteries, suggesting a potential role in the maintenance of cardiovascular health.