New techniques for the measurement of cardiac output, which have been advocated for their minimal invasiveness or continuous mode of analysis or both, are now being critically evaluated in clinical practice. Ventricular pressure-volume and pressure-flow analysis have generated improved indexes of cardiac performance and have led to a better understanding of ventriculo-vascular couplilng. Assumptions required for non-invasive measurement of ventricular pressures and volumes, and the absence of simple on-line analysing techniques remain the major limitations to their standard clinical use.