Critical care nurses frequently are involved in obtaining cardiac output measurements and in using these data to assess and to plan therapy. This article reviews the physiologic determinants of cardiac output and the clinical factors that influence these determinants. Principles and techniques of common methods of cardiac output measurement are discussed. A thorough presentation of guidelines for troubleshooting problems with thermodilution cardiac output measurement is provided in a table. Nursing management issues are discussed using relevant nursing research. Future considerations in cardiac output measurement are discussed, and suggestions of an ideal cardiac output system are provided