It has long been known that exposure of blood to the heart-lung bypass machine can trigger a whole-body inflammatory response in cardiac surgery patients that is linked to activation of circulating white blood cells. The investigators propose to use a technique to track the movement of white blood cells into the skin of patients during bypass surgery. The skin blisters will be elicited by application of the blistering agent cantharidin to the forearm of volunteer patients. This will allow the investigators to study the activation state of white blood cells that enter tissues during bypass surgery and to determine whether aprotinin has any beneficial effect with regards to inflammatory status of these cells.