Aromatase inhibitors are the most used endocrine therapy for hormone-positive breast cancer. While there is a clear linear relationship between the duration of aromatase inhibitor use and the cumulative incidence of cardiovascular events and mortality, the underlying mechanisms contributing to this risk remain unknown. This study will characterize the short-term effects of aromatase inhibitor therapy on established and novel health indices for cardiovascular diseases in breast cancer patients. Using a longitudinal case-control design this study will assess the effects of short-term (first 6 months) aromatase inhibitor use in breast cancer patients compared to age- and BMI-matched controls, aiming to determine the cardiovascular, metabolic, and behavioural health impacts of endocrine treatment during this early period. Specifically, our objectives are as follows: 1. To examine the effects of aromatase inhibitor therapy on early risk indicators for cardiovascular disease in the peripheral vasculature and heart, including blood biomarkers (lipids), blood pressure, aortic and peripheral stiffness, carotid artery stiffness and intima media thickness, endothelial function, and left ventricular ejection fraction, longitudinal strain, volumes, and mass, including the responsiveness of the cardiovascular system to an oral glucose tolerance test, in breast cancer survivors compared to controls. 2. To examine the effects of aromatase inhibitor therapy on factors related to cerebrovascular health, autonomic regulation, and cognitive function, including BDNF, heart rate variability, cerebrovascular function in response to a supine-sit-stand maneuver and squatting challenge, and a core battery of cognitive function tests, in breast cancer survivors compared to controls. 3. To examine the effects of aromatase inhibitor therapy on body composition and bone mineral density, along with assessments of glycemic regulation in response to an oral glucose tolerance test and in 24h periods of free-living (continuous glucose monitoring), in breast cancer survivors compared to controls. 4. To examine the effects of aromatase inhibitor therapy on lifestyle factors (behavioural), including diet, physical activity (including cardiorespiratory fitness), sleep, stress, and quality of life, in breast cancer survivors compared to controls. The investigators hypothesize that cardiovascular and metabolic health outcomes will be similar between breast cancer survivors and controls at baseline but will deteriorate relative to controls within the first 6 months of aromatase inhibitor therapy.