From the earliest days of critical care medicine, the importance of measuring cardiac output and hemodynamic monitoring were recognized in understanding the physiology of critically ill patients, especially those in shock. However, methods for measuring cardiac output were cumbersome or not widely available. Ashish K. Khanna, MD, FCCP, FCCM, is joined by Margaret M. Parker, MD, MCCM, to discuss the evolution of the pulmonary artery catheter in critically ill patients, as discussed in "The Story of the Pulmonary Artery Catheter: Five Decades in Critical Care Medicine," published in the February issue of Critical Care Medicine (Parker M et al. Crit Care Med. 2023;51:159-163). Dr. Parker is professor emeritus of pediatrics at Stony Brook University School of Medicine in Stony Brook, New York, USA.