Cardiac catheterization includes studies of the right side of the heart, the left side of the heart, and the coronary arteries. Special catheters (thin, flexible tubes) are inserted into blood vessels in the groin or arm. X-ray is used to help the doctor thread the catheters into the heart. The doctor can check pressures inside of the heart and can also inject contrast (dye) into the coronary arteries (the arteries that supply blood to the heart muscle). This test is a valuable diagnostic tool for getting information about the structure and function of the heart chambers, valves, great vessels, and coronary arteries.