Since there is increasing interest in the use of both pulse pressure variation (PPV) and stroke volume variation (SVV) to predict preload responsiveness and drive resuscitation protocols, Mesguida et al. [106] evaluated the impact of increasing tidal volume, decreased chest wall compliance, and left ventricular contractility during intermittent positive-pressure ventilation (IPPV) on the relation between PPV and left ventricular stroke volume variation and intrathoracic blood volume changes in dogs. This study provides a systematic examination of the changes in the right and left heart pressure and stroke volumes during the ventilator cycle. The author's major conclusion is that there is tight coupling between pulse pressure and left ventricular SVV. The authors have also added some important new information that shows the effect of changes in chest wall compliance, tidal volume and left ventricular function on the measurements. It is noteworthy that a proper quantitative analysis would require integrating the area under the stroke volume curves of all the stroke volumes in inspiration and expiration. What the author is really showing is that there are transient differences between the right and left side peak stroke volumes that must be associated with gains or losses of pulmonary vascular volume to fulfil the conservation of mass.