A catheter is a thin, flexible, hollow plastic tube that can be used to perform various diagnostic and/or therapeutic procedures. Catheters may be used for injection of fluids or medications into an area of a body or for drainage, such as from a surgical site. They are also frequently used to allow physicians to access the body with surgical instruments.

Catheters are designed to gain access to the body with as little trauma as possible. For this reason, catheter-based therapies are sometimes called minimally invasive. The process of introducing a catheter is known as catheterization. When it involves the heart, the procedure is known as cardiac catheterization.

Cardiovascular catheters are small enough to be threaded through a vein or artery and all the way to the heart. Patients generally do not feel the movement of the catheter through their body. Once in place, the catheter allows a number of tests and/or treatment procedures to be performed, including angiography or balloon angioplasty.