Cardiac output monitoring in the critically ill patient is standard practice in order to ensure tissue oxygenation [1] and has been traditionally accomplished using the pulmonary artery catheter (PAC). In recent years, however, the value of PAC has been questioned with some suggesting that its use might not only be unnecessary but also potentially harmful [1]. This notion, together with the availability of new less invasive cardiac output measuring devices, has markedly decreased the widespread use of the PAC [2]. Today, various devices are available to measure or estimate cardiac output using different methods. Some of these less invasive devices track stroke volume (SV) continuously and provide dynamic indices of fluid responsiveness, others allow assessment of volumetric preload variables, and some also provide continuous measurement of central venous saturation via the use of proprietary catheters that are attached to the same monitor. All these variables — together with cardiac output — may result in an improved hemodynamic assessment of the critically ill patient. However, it is important to appreciate that each device has its inherent limitations and that no cardiac output monitoring device can change patient outcome unless its use is coupled with an intervention that by itself has been associated with improved patient outcomes. Therefore, the concept of hemodynamic optimization is increasingly recognized as a cornerstone in the management of critically ill patients and has been shown to be associated with improved outcome in the perioperative [3] and in the intensive care unit (ICU) [4] setting.