Everyone has collateral vessels, at least in microscopic form. These vessels aren't open under normal conditions but grow and enlarge in some with coronary heart disease. When a collateral vessel enlarges, it lets blood flow from an open artery to either an adjacent artery or further downstream on the same artery. R esearch has shown that while everyone has collateral vessels, they don't open and become available in all people. People who have open collateral vessels can benefit, because collateral vessels help protect heart muscle from tissue death if the normal blood supply is cut off.
High levels are a large factor in clogging arteries.
Your blood pressure is checked each time you donate and cholesterol levels are checked periodically.