This is an invasive procedure, which is performed under sterile conditions in a cardiac catheterization laboratory (cath lab). The procedure may or may not be performed under general anesthesia. In any event, the patient is sedated and usually asleep. During this test, a thin, flexible tube (catheter) is inserted into a blood vessel at the groin or arm. The catheter is then advanced, under radiographic vision, into the heart. Blood samples are obtained at different parts of the heart in order to check the oxygen levels. In addition, blood pressures are determined at the heart chambers and blood vessels. A radiographic liquid is injected into the flexible catheter by hand pressure, or more often, by using a special pressurized machine. The radiographic liquid is delivered into the heart or heart vessels. It is then recorded on a video or computerized digital system and images are obtained. That way, we can check for leaky valves, obstructed valves, holes in the heart, a communication outside the heart between the great arteries, coronary abnormalities, and many other heart conditions.