Passive leg raising (PLR), by inducing a gravitational transfer of blood from the lower part of the body toward the central circulatory compartment, can be considered as a brief "self volume challenge". Recently, a systemic review and meta-analysis concluded that PLR-induced changes in cardiac output reliably predict fluid responsiveness regardless of ventilation mode, underlying cardiac rhythm and technique of measurement and can be recommended for routine assessment of fluid responsiveness in the majority of ICU population. More importantly, this prediction remains very valuable in patients with cardiac arrhythmias or spontaneous breathing activity.