Cardiac output monitoring in the cardiac surgery patient is standard practice that is traditionally performed using the pulmonary artery catheter. However, over the past 20 years, the value of pulmonary artery catheters has been challenged, with some authors suggesting that its use might be not only unnecessary but also harmful. New minimally invasive devices that measure cardiac output have become available. In this paper, we review their operative principles, limitations, and utility in an integrated approach that could potentially change patients' outcome. However, it is now clear that it is how the monitor is used (ie, the protocol or therapy associated with its use, or its lack thereof), and not the monitor per se, that should be questioned when a patient's outcome is being evaluated.