A cardiac cath is done in the hospital. The doctor will insert a tiny catheter into an artery near your groin where they can follow that all the way up to your heart. A dye is injected and pictures are taken as the dye is passing through the arteries. Anywhere the dye narrows shows a blockage in your artery. Typically a blockage can be fixed with a stent, which as explained above is a balloon that is inster that will open the artery back up.