Bedside evaluation of pulmonary mechanics and thoracic computed axial tomography have changed the ventilatory management of patients suffering an acute respiratory failure caused by adult respiratory distress syndrome (ARDS). Mortality has been reduced limiting tidal volumes, which avoids alveolar overdistention and by the use of positive end expiratory pressure (PEEP), that reduces the damage caused by cyclical alveolar collapse-reopening. Nowadays, it is well known that inappropriate mechanical ventilation enhances lung damage caused by the underlying disease. However, the optimal adjustment of PEEP is not yet established. Usually, it is not easy to achieve an equilibrium between an optimal lung recruitment without producing alveolar overdistention and hemodynamic adverse effects such as hypotension and reduction of cardiac output. This paper reviews the interactions between heart and lung (Rev Méd Chile 2002; 130: 1419-30)