Transudative pleural effusions are a common manifestation of patients with congestive heart failure. Severe dyspnea and respiratory failure may develop in those with large effusions, which in general show poor response to medical treatment. Therapeutic thoracenteses (TT) may be indicated in these patients and can produce marked relief of symptoms. However, the underlying effect of TT on gas exchange and respiratory mechanics in theses patients remains unclear. The researchers' hypothesis is that,TT may improve arterial oxygenation and respiratory mechanics in patients with congestive heart failure complicated by large pleural effusions.

Inclusion Criteria:

• transudative pleural effusion established by the criteria of Light
• the effusion occupying at least half of one hemithorax shown on chest radiography
• symptoms of respiratory distress
• diagnosis of congestive heart failure

Exclusion Criteria:

• severe uncontrolled coagulopathy
• unstable hemodynamics
• diagnosis of liver cirrhosis, chronic obstructive pulmonary disease,asthma and/or any parenchymal lung disease, such as pneumonia, fibrosis or malignancy.