Study participants will take three aspirin tablets. After administration of a local anesthetic, small tubes will be inserted through a needle into the artery and vein of the forearm. These will be used to measure blood pressure and to draw blood samples during the study. Forearm blood flow will be measured using pressure cuffs placed on the wrist and upper arm, and a strain gauge (a rubber band device) placed around the forearm. When the cuffs are inflated, blood will flow into the arm, stretching the strain gauge, and the flow measurement will be recorded.