3. Endothelial-dependent vasodilation using brachial artery diameter will be measured by ultrasound. A blood pressure cuff will be inflated on the arm to a supra-systolic pressure for 5 minutes. This results in vasodilation of the downstream blood vessels. Following release of the cuff, there is usually a 6 to 10-fold increase in flow through the brachial artery, i.e., reactive hyperemia. Flow is a physiologic stimulus that releases nitric oxide and causes dilation of the brachial artery, and hence, an increase in the diameter of the brachial artery; this can be measured using ultrasound. The maximal increase in brachial artery diameter occurs at one minute of reactive hyperemia and this dilation is mediated by nitric oxide. Endothelium-independent vasodilation (as a positive control) will be assessed by measuring brachial artery diameter under basal conditions and 3 minutes following the administration of sublingual nitroglycerin (0.4 mg). Maximal brachial artery dilation occurs 3 to 4 minutes after the administration of sublingual nitroglycerin.