Hepatopulmonary syndrome is characterized by the presence of portal hypertension with or without cirrhosis, an increased alveolar-arterial oxygen partial pressure difference greater than or equal to 15 mm Hg, and dilated pulmonary capillaries. Hepatopulmonary syndrome is found in up to 20% of patients with cirrhosis and should be considered in any patient who develops dyspnea or hypoxemia. Contrast echocardiography is enough to make the diagnosis of hepatopulmonary syndrome. The exact pathophysiology of hepatopulmonary syndrome remains unknown but nitric oxide is an important factor underlying hepatopulmonary syndrome. Hypoxemia progressively deteriorates and worsens the prognosis of cirrhotic patients. Hypoxemic patients must be controlled regularly to optimise the timing of liver transplantation. Indeed, a preoperative PaO(2) of less than or equal to 50 mm Hg alone or in combination with an isotopic shunt fraction greater than or equal to 20% are the strongest predictors of postoperative mortality. There are currently no effective medical therapies for hepatopulmonary syndrome but garlic powder and iloprost inhalation demonstrate clinical improvements in the pre- and in the post-transplant period.