Diagnostic cardiac catheterization is the best way to diagnose the patient’s heart problem. During a diagnostic cardiac catheterization, the patient is under anesthesia or under sedation. Next, hollow plastic tubes called catheters are introduced into the veins and/or arteries in the leg or neck, from which they are advanced to the right and/or left sides of the heart. Once the catheters are positioned in the various heart chambers or blood vessels, the pressure of the blood can be measured, blood samples can be taken and dye (radiographic contrast material) can be injected (a process called angiography) to allow X-ray visualization. Diagnostic cardiac catheterization can be used to clarify a confusing or unclear situation in a patient whose clinical findings and noninvasive testing are unclear. Finally, it can confirm a suspected abnormality in the patient for whom heart surgery is planned and exclude associated abnormalities that might require the surgeon’s attention.