There are two basic reasons a cardiac catheterization might be done. The first reason is to gain critical information about the heart and major arteries before surgery, as well as to clearly see the source of the problem in the patient. This helps physicians plan any upcoming procedure. Specific examples include:

• Determining whether someone is a good candidate for surgery (e.g., a bypass surgery) or other procedures
  
  
• Detecting any other heart defects that may be present before doing surgery to correct a heart defect
  
  
• Getting a clear picture of a heart defect before surgically correcting it, or to determine whether surgery is necessary

The other basic reason cardiac catheterization would be done is to help make a diagnosis of a suspected cardiac problem, especially coronary artery disease. Other conditions that may be detected by cardiac catheterization include:

• Pulmonary hypertension. High blood pressure in the lungs, often due to cardiac abnormalities.
  
  
• Pulmonic valve stenosis. A condition when the pulmonic valve, which regulates blood flow from the right ventricle to the pulmonary arteries, is partially blocked.
  
  
• Pulmonary embolism. A condition when a blood clot has caused restricted blood flow inside the lungs.
  
  
• Congenital defects. Cardiac catheterization can be used to confirm certain heart defects present at birth, including tetralogy of Fallot, transposition of the great arteries, tricuspid regurgitation and ventricular septal defect, atrial septal defect. 
  
  
• Other heart valve problems. These may include stenosis (narrowing) or regurgitation of any of the heart valves.  

Cardiac catheterization is usually done after other tests have been performed. These tests include:

• Electrocardiogram (EKG). An EKG is a recording of the heart’s electrical activity as a graph on a moving strip of paper. The highly sensitive electrocardiograph machine helps detect heart irregularities, disease and damage by measuring the heart’s rhythms and electrical impulses.
  
  

• Echocardiogram of the heart. This test uses sound waves to visualize the structure and function of the heart. A moving image of the patient’s beating heart is displayed on a video monitor, where a physician can study the heart’s thickness, size and function. The image also shows the motion pattern and structure of the four heart valves, revealing any potential leakage regurgitation. During this test, a Doppler ultrasound may be done to evaluate blood flow through the heart valves.
  
  

  
  

• Exercise stress test. An EKG is performed while the patient exercises in a controlled manner on a treadmill or stationary bicycle at varied speeds and elevations. The reaction of the heart under exertion can be measured and evaluated. This test may be done in conjunction with an echocardiogram (as described above) or nuclear imaging (a nuclear stress test).
  
  
• Computed tomography scan, or CT scan. This test uses x-ray technology and multiple sensors to create very accurate, three-dimensional images of the heart. Advances in CT technology have made this an important diagnostic tool that, together with magnetic resonance imaging (see below), has reduced the need for cardiac catheterizations.