Pressure monitoring systems influence the contour of the displayed wave-forms and, on occasion, can introduce significant artifact in the pressure traces. It is important to understand the technical details of invasive pressure monitoring to interpret better the information presented. Careful observation of the arterial pressure waveform can provide information about ventricular function, the arterial system, and ventricular preload. In particular, systolic pressure variation during the respiratory cycle in mechanically ventilated patients is a clinically useful indicator of volume status. CVP monitoring is also used to assess intravascular volume, but this measurement is significantly influenced by ventricular compliance and intrathoracic pressure. Under most clinical circumstances, a trend in CVP values or its change with therapeutic maneuvers is more reliable than a single measurement. Like arterial pressure waveforms, CVP waveform morphology can provide important information about clinical pathophysiology.