Cardiac catheterization (heart cath) is the insertion of a catheter into a chamber or vessel of the heart. This is done for both diagnostic and interventional purposes. Subsets of this technique are mainly coronary catheterization, involving the catheterization of the coronary arteries, and catheterization of cardiac chambers and valves.
Coronary catheterization 
Local anaesthetic is injected into the skin to numb the area. A puncture is then made with a needle in either the femoral artery in the groin or the radial artery in the wrist, (Seldinger technique), before a guidewire is inserted into the arterial puncture. A plastic sheath (with a stiffer plastic introducer inside it) is then threaded over the wire and pushed into the artery. The wire is then removed and the side-port of the sheath is aspirated to ensure arterial blood flows back. It is then flushed with saline. This arterial sheath, with a bleedback prevention valve, acts as a conduit into the artery for the duration of the procedure.
Catheters are inserted using a guidewire and moved towards the heart. Once in position above the aortic valve the guidewire is then removed. The catheter is then engaged with the origin of the coronary artery (either left coronary artery or right coronary artery) and x-ray opaque iodine-based contrast is injected to make the coronary vessels show up on the x-ray fluoroscopy image.
When the necessary procedures are complete, the catheter is removed. Firm pressure is applied to the site to prevent bleeding. This may be done by hand or with a mechanical device. Other closure techniques include an internal suture and plug. If the femoral artery was used, the patient will probably be asked to lie flat for several hours to prevent bleeding or the development of a hematoma. If the arm is used, the patient can ambulate sooner. Cardiac interventions such as the insertion of a stent prolong both the procedure itself as well as the post-catheterization time spent in allowing the wound to clot. However, the femoral artery is associated with local complication in up to 3% of patients and hence, more interventional physicians are moving towards the radial (wrist) artery, as an alternative site. Disadvantages of the radial artery include small vessel caliber and a different "learning curve" for physicians used to the femoral (groin) access.
"Cardiac catheterization" is a general term for a group of procedures that are performed using this method, such as coronary angiography, as well as left ventricle angiography. Once the catheter is in place, it can be used to perform a number of procedures including angioplasty, PCI (percutaneous coronary intervention) angiography, balloon septostomy, and an Electrophysiology study or Catheter ablation.
Indications for diagnostic use 
This technique has several goals:
- confirm the presence of a suspected heart ailment
- quantify the severity of the disease and its effect on the heart
- seek out the cause of a symptom such as shortness of breath or signs of cardiac insufficiency
- make a patient assessment prior to heart surgery
Investigative techniques used with coronary catheterization 
- to measure intracardiac and intravascular blood pressures
- to take tissue samples for biopsy
- to inject various agents for measuring blood flow in the heart; also to detect and quantify the presence of an intracardiac shunt
- to inject contrast agents in order to study the shape of the heart vessels and chambers and how they change as the heart beats
Catheterization of chambers and valves 
Catheterization of cardiac chambers and valves may be performed in the same round as a coronary catheterization, and may also involve nearby major vessels, such as the aorta. It is the main method of cardiac ventriculography (another being radionuclide ventriculography, whose use has largely been replaced by echocardiography).
The history of cardiac catheterization dates back to Claude Bernard (1813-1878), who used it on animal models. Clinical application of cardiac catheterization begins with Werner Forssmann in the 1930s, who inserted a catheter into the vein of his own forearm, guided it fluoroscopically into his right atrium, and took an X-ray picture of it. Forssmann won the Nobel Prize in Physiology or Medicine for this achievement, though hospital administrators removed him from his position owing to his unorthodox methods. During World War II, André Frédéric Cournand, a professor at Columbia University College of Physicians and Surgeons who also shared the Nobel Prize, and his colleagues developed techniques for left and right heart catheterization.
- MedlinePlus Medical Encyclopedia: Cardiac catheterization
- eMedicine: Cardiac Catheterization (Left Heart)