This procedure involves insertion of a long, thin, flexible catheter into the arm, groin or neck, which leads to the heart. The catheter introduces an x-ray dye into the coronary arteries of the heart (coronary angiography). This shows where arteries may be possibly blocked or narrowed by plaque made up of fat, cholesterol, calcium and other substances found in the blood stream. These substances can limit blood flow to the heart and can cause symptoms like chest pain and shortness of breath and eventually result in a heart attack.  In some cases, it is not enough to view the blockage. Doctors may need a blood or heart muscle sample and they can do it through the catheter. This procedure is considered very safe and effective. Patients are not given any anesthesia and are not put to sleep. It is also relatively painless, with some patients experiencing discomfort in the area that the catheter is inserted.