Continuous positive airway pressure, like positive end-expiratory pressure (PEEP), increases lung volume and pleural pressure and usually decreases venous return. The decrease in venous return has been ascribed to a simple increase in right atrial pressure. However, recent studies have demonstrated PEEP also changes the resistive and elastic properties of peripheral veins. PEEP elevates the upstream pressure driving venous return, increases venous resistance, and directly compresses the inferior vena cava. The dogma that PEEP decreases venous return by decreasing the pressure gradient driving blood from the systemic vessels to the heart appears to be untrue.