A concept known as pre-conditioning has been identified as a phenomenon that limits the extent and severity of reperfusion injury. Classically, preconditioning refers to the occurrence whereby repeated brief episodes of ischemia preceding a prolonged period of ischemia results in marked diminution of ischemic injury and injury occurring during reperfusion. The mechanism of this ischemic tolerance was thought to be secondary to the recruitment of collateral circulation, as it was noted to develop in patients undergoing serial balloon inflations during angioplasty. The cellular mechanism involved in ischemic preconditioning are not completely understood, but may be related to the attenuation of reperfusion injury. These findings are also corroborated by Kharbanda's group in their findings made after inducing forearm ischemia in 31 healthy volunteers. In an attempt to test the effects of ischemic preconditioning on the attenuation of ischemia-reperfusion injury as it pertains to endothelial function and circulating blood cell function, the forearms of these volunteers were made ischemic for a 20 minutes period using a pneumatic blood pressure cuff to 200 mmHg. This method was then compared to the use of ischemic preconditioning prior to the prolonged 20 minutes ischemic episode. Ischemic preconditioning was induced by inflating the pneumatic cuff to 200 mmhg for 5 minutes and then deflating the cuff. This was repeated for a total of 3 times. Radial artery reactivity testing and blood samples were collected from the antecubital vein at timed intervals after cuff deflation in both methods. It was noted that ischemic -preconditioning prior to prolonged forearm ischemia prevented both endothelial dysfunction and neutrophil activation.