A thin long tube made of flexible silicone rubber that is surgically (in an operating room) inserted into one of the main blood vessels leading to the heart. The catheter can be used for drawing blood samples and for giving intravenous fluids, blood, medication, or nutrition. It is often put in to improve nutrition and monitor heart function or for long term treatments. It may decrease the number of needle sticks needed to draw blood and is often used when IV's are not otherwise available.