Monitoring of Cardiac Output (CO) is of paramount importance in the critical patient. Established methods used to measure CO, such as oxygen Fick approach and thermodilution, are invasive and do not allow continuous monitoring. In addition, they are not reliable in the hemodynamically instable patient and suffer several technical drawbacks. Alternative methods are available, such as the Pulse Contour Method, but are dependent upon external calibration to evaluate cardiac activity. Recently, the Pressure Recording Analytical Method (PRAM) has been developed: it allows a more complete and detailed analysis of pressure morphology and "beat-to-beat" measurement of the stroke volume (SV) without external calibration. The basic principle of PRAM algorithm is the ability of detecting interactions between the cardiac and circulatory system, and therefore of calculating a new parameter, describing the work expenditure of cardiovascular system strictly correlated to SV, the Cardiac Cycle Efficiency (CCE). PRAM is becoming a promising alternative to traditional techniques, and may expand the potential applications of hemodynamic monitoring in clinical practice.