A catheter (CATH-uh-ter) is a thin, hollow tube that's inserted in the body, so it can deliver or carry away some substance. In cardiac catheterization (cath-uh-ter-eye-ZAY-shun), the tube is inserted through a blood vessel in the groin, and guided by x-ray to the heart. Typically, a special dye is then introduced into the tube, where it travels to the coronary arteries. This procedure is known as coronary angiography (ann-jee-OG-rah-fee). Doctors can trace the path of the dye on the x-ray monitor, thus discovering any blockages. In addition, they may gather information on the heart's overall function, including blood flow and valve operation. Cardiac catheterization is relatively painless, and is performed in the lab under mild sedation. After the nurse removes the catheter, pressure is applied for about 30 minutes to stop bleeding at the site. The patient usually spends the day resting in bed. While the procedure is not without risk, it remains the most effective test available for diagnosing heart disease and assessing treatment options. It's particularly useful for patients who may need balloon angioplasty or open-heart surgery. For complete information on cardiac catheterization, speak with a cardiologist or health care professional.