Cardiac catheterization is a common – yet potentially lifesaving – procedure that is performed to diagnose and treat blocked arteries. A narrow tube called a catheter is inserted into the artery through a vein in the leg and threaded upwards to the heart. Using a special x-ray camera called a fluoroscope and radiopaque dye, which shows how blood passes through the heart and surrounding vessels, doctors can see fat and calcium deposits (plaque) that may be blocking circulation. While cardiac catheterization is helpful in determining whether a person needs bypass surgery, doctors can sometimes clear the blockage during the procedure using balloon angioplasty or stenting.