See Youtube link  in endnotes for animation of pulmonary arterial catheter (PAC) traversing the heart along with the associated wave forms. Screen captures are provided in this blog post.
PACs measure intracardiac filling pressures.
PA wedge pressure approximates LA pressure.
This Youtube video  (from NEJM) explains the procedure, indications and contraindications of PAC insertion as well as interpretation of values derived from the PAC in different disease states.
INDICATIONS. PACs can be used to diagnose pulmonary hypertension, cardiogenic shock, mixed shock states, cardiac tamponade and mechanical complications of STEMI. It is also part of the standard evaluation for heart and lungs being considered for transplantation.
INAPPROPRIATE USE. PACs should not be used as part of routine treatment for patients undergoing high risk surgery, or for patients with septic shock, ARDS or acute decompensated heart failure as RCTs have shown no benefits and possible harm. In these cases, evaluation non invasive means is recommended – including physical examination, serum BNP levels, echocardiography, US of IVC and/or assessment of pulse-pressure variation during respiration.
CONTRAINDICATIONS: Absolute contraindications to insertion of PACs include R-sided infective endocarditis and R-sided thrombus or masses. Relative contraindications include severe coagulopathy and severe thrombocytopenia. Caution should be exercised in PAC insertion in patients with tricuspid regurgitation (where it may be difficult to traverse through the tricuspid valve) and in the presence of a LBBB (where PAC insertion may induce a complete heart block).
THE STANDARD CATHETER:
NOTE: Use only syringe packaged with the catheter. Balloon should be inflated whenever the catheter advanced and deflated whenever it is withdrawn.
 YouTube,. “Swan Ganz Physiology” by Edwards Corporation. N.p., 2016. Web. 7 Feb. 2016. https://www.youtube.com/watch?v=7putxZN7ij4
 YouTube,. “Pulmonary-Artery Catheterization”. N.p., 2016. Web. 7 Feb. 2016. https://www.youtube.com/watch?v=6D_ihQZ2e-M