In heart failure lung dysfunction is frequent and is greater the greater the heart failure severity. It can be evaluated in terms of lung mechanics and gas diffusion. Indeed heart-lung interaction is related to heart dimensions and lung fluid content; furthermore heart-lung interaction is influenced by the body position. Lung diffusion is also altered in patients with chronic heart failure, and a low gas diffusion is associated with a reduced performance. During exercise, heart-lung interaction becomes more evident. Heart failure patients show an abnormal hyperventilation due to a progressively increased respiratory rate, and a lower tidal volume; hyperventilation is due to different causes including enhanced responses from chemo- and metabolo-receptors, increased CO(2) production and increased dead space ventilation. Several drugs affect the ventilatory pattern in heart failure patients: ACE-inhibitors and anti-aldosteronic drugs improve lung diffusion and ventilatory efficiency during exercise; beta-blockers reduce exercise-induced hyperventilation. Furthermore, ultrafiltration improves lung mechanics, both at rest and during exercise, through body fluid content reduction.