Cardiac catheterization is a minimally invasive procedure in which a long, thin tube called a catheter is guided into the heart, usually through a blood vessel in the leg or arm. Once inside the heart, it can be used to diagnose a problem (diagnostic uses) or to treat a problem (therapeutic uses). This article deals with the diagnostic uses of cardiac catheters.

By gaining access to the beating heart, cardiac catheters allow a physician to check the internal blood pressure of the heart, assess blood supply, view the coronary arteries on the surface of the heart and (depending on where the catheter is placed) the aorta, monitor the electrical activity in the heart, and check the level of oxygen in the blood. It is also used to evaluate the ability of the pumping chambers to contract, as well as to assess the function of heart valves. Cardiac catheterization is one of the most accurate tests in the diagnosis of coronary artery disease, and over a million of them are done each year. 

During cardiac catheterization, the catheter is inserted through a very small cut made by the physician (in the groin, arm or wrist), then guided up through the blood vessel to the heart. The physician tracks the course of the catheter by watching it on a fluoroscope, an x-ray machine that displays the catheter and blood vessels in real time on a screen. A variety of measurements may be performed when the catheter is in place, and then the catheter is removed. After some recovery time, most patients are free to go home after about six hours. Results are available to the physician immediately.