The application of a positive end-expiratory pressure (PEEP), the cornerstone of noninvasive ventilation (NIV), causes hemodynamic changes in the cardiovascular system. To understand the benefits of NIV it is necessary to resume concepts of cardiovascular physiology and pathophysiology about cardiac function determinants, venous return, ventricular interdependence and heart-lung interaction, and to understand how PEEP interacts with them. The hemodynamic effects of PEEP are mediated by the increase in transpulmonary pressure, which results in increased pulmonary vascular resistance and in an attending small reduction of venous return in conditions of euvolemia, in a substantial reduction of left ventricular afterload and a potential positive effect on left ventricular stroke volume.The aim of this review is to describe how the application of PEEP does not necessarily induce detrimental hemodynamic effects, but may decrease oxygen consumption and improve cardiac performance. These effects can justify the use of NIV in hemodynamically unstable patients.