Swan ganz catheters are long hollow plastic tubes. It allows direct measurement of intravascular pressures in the right heart and pulmonary artery, as well as sampling of mixed venous blood. Left atrial pressure can be assessed indirectly with these catheters using the pulmonary artery wedge pressure, also referred to as pulmonary artery occlusion or pulmonary capillary wedge pressure. It is placed inside the neck or the shoulder. It is a thin, flexible tube that is inserted through one of the large veins that return blood to the heart. The catheter is flow-directed. It uses a balloon to carry it through the vena cava to the heart, through the right side of the heart to the pulmonary artery.