In this study we examined the relationship between cardiac output (CO) measurements obtained from the proximal injectate lumen and the proximal infusion lumen of a thermodilution pulmonary artery catheter. The research was predicated on the belief that a strongly significant relationship would provide the clinician with an alternative lumen for measuring CO. Twenty-one subjects were selected by using a nonprobability convenience sampling method. With ice temperature injectate, four injections were performed into one lumen followed by four injections into the alternate lumen. CO values were computed with installed data management physiologic monitors. A Pearson's Product-Moment Correlation Coefficient was calculated, and the result verified a strong positive correlation between CO values (r = 0.96, p = less than 0.0001). Results of a paired t test demonstrated no statistically significant differences between CO means. These findings lend direction for minimizing the potential risk of catheter contamination associated with the manipulation of intravenous lines containing vasoactive medications. It also may save time for the critical care clinician who is trying to balance tasks such as CO measurements and titration of vasoactive or inotropic medications.