Polycystic ovary syndrome (PCOS) affects 1 in 5 females of reproductive age. Commonly characterized as a disorder of infertility, PCOS is often accompanied by 3 potent cardiovascular disease (CVD) risk factors: insulin resistance, endothelial dysfunction, and elevated blood pressure. Accordingly, PCOS is associated with the development of CVD, the second leading cause of death in females in Canada. However, effective treatments to improve cardiovascular health in PCOS are lacking. Exogenous ketone monoester (KME) ingestion has been shown to improves outcomes associated with insulin resistance, endothelial function, and blood pressure regulation in healthy individuals and individuals predisposed to CVD. Therefore, oral ketone supplements offer a practical and effective strategy for improving cardiovascular health; however, this treatment has yet to be evaluated in PCOS. Therefore, the overall goal of this project is to employ KME ingestion to improve markers of cardiovascular health in females with PCOS. On two different days, participants will consume either a beverage containing a ketone supplement or a beverage containing a placebo supplement. The objectives are to compare responses between KME and placebo ingestion, and examine all outcomes related to cardiovascular health in females with PCOS in comparison with female controls of similar age and body mass index. The effects of KME ingestion will be quantified on: 1) glycemic control during an oral glucose tolerance test; 2) endothelial function using the flow-mediated dilation test; 3) blood pressure and acute blood pressure regulation; and 4) hemodynamic responses to acute exercise.