A fluoroscopic image of the chest in the supine position illustrates zones used to classify catheter tip location. Cavoatrial junction (CAJ) is defined as the height of 2 vertebral body levels below the level of the carina (dotted line). The area between half vertebral body levels above and below the CAJ is considered a proper position of the tip (Zone 2). Above and below Zone 2 is located in superior vena cava (Zone 1) and right atrium (Zone 3).