The pulmonary artery catheter (PAC) was adopted about 36 years ago and is now commonly used in intensive care units (ICUs). The PAC is used to diagnose various diseases or physiological states, monitor the progress of disease, and guide the selection and adjustment of medical therapy in critically ill patients. Clinicians consider the use of a PAC to be beneficial. There have been many studies regarding the impact of the PAC in critically ill patients over the last 20 years. Most data fromobservation studies have shown that patients who have undergone a PAC placement have had a higher mortality rate, but these patients were also more gravely ill, both in terms of acute severity of illness and chronic comorbid medical conditions. Therefore, a randomized controlled trial was designed to determine the efficacy of the PAC, in which it was found that use of the PAC neither increased mortality nor conferred any real benefit. Thus, PAC use should not be routine in critically ill patients but should serve a specific purpose consistent with clinical decision making.