Hemodynamic monitoring is the main component in intensive care unit (ICU). Patients in ICU are under hemodynamic instability and multi-organ failure for some hours or even some days. Volume – pressure relation constitutes the most reliable method for the estimation of central hemodynamic state and ventricular function. Therefore, the evaluation of intracardiac volume and pressure is necessary. However no available method exists for clinical use that measures the volume of the right ventricular cavity continuously in real time. This paper discusses the methods could be used in measuring the right ventricular volume in the context of an efficient cardiac function evaluation of critical ill patients in ICU, using miniaturised ultrasound on the tip of a Pulmonary Artery Catheter (PAC), which is anyway used on that purpose but evaluates only pressure.