The pulmonary wedge pressure (PWP) or wedge pressure is an indirect estimate of the pressure in the left atrium of the heart. A Swan-Ganz catheterization, also known as pulmonary artery catheterization (PAC), during which a catheter is placed directly into the pulmonary artery to measure the pressure in the right atrium, right ventricle, pulmonary artery, and the wedge pressure of the left atrium. It is also possible to measure pressure in the left atrium directly, but placing a pressure catheter directly through the “coronary sinus” (venous connection between right and left atrium) is a difficult and uncommon procedure.