The resuscitation of critically ill patients frequently requires the administration of fluids for the purpose of increasing cardiac output and oxygen delivery to the tissues. The assessment of the patient’s preload status during this process is vital. Traditionally, preload assessment has been through the use of right atrial pressure and pulmonary artery occlusion pressure, which are often referred to as the “filling pressures.” The use of these filling pressures is based upon the assumption that ventricular compliance does not change. In recent years studies have demonstrated a poor correlation between these pressures and cardiac output. More recently, the ability to measure right ventricular end-diastolic volume (RVEDV) at the bedside using a modified pulmonary artery catheter became available. Initially the measurement was obtained using intermittent bolus measurements. Today, near continuous measurements of RVEDV are available. The shift from using pressure measurements for the purpose of assessing preload to the new paradigm of using right ventricular volumetric measurements is challenging. The purpose of this article is to review pertinent anatomy of the right ventricle and the interdependence of the ventricular chambers. The volumetric parameters are presented followed by a discussion of research supporting the use of the volumetric parameters in lieu of pressure measurements for preload assessment in a variety of patient populations. The technology providing continuous RVEDV measurements is presented followed by a discussion of a case study demonstrating the value of continuous measurements. Specific implications for the advanced practice nurse are addressed.