The physiologic basis for relief from dyspnea after therapeutic thoracentesis remains poorly understood. Improvement of the heart and lung function may contribute to the dyspnea relief. But there is no data support this phenomenon. Transthoracic echocardiogram (TTE) is a non-invasive viewing of the heart, which can quickly assess the heart function through real-time images. The investigators performed thoracentesis on patients with large-volume pleural effusions, and utilized TTE to access the change of heart and lung function before and after this medical procedure.

Patients with large pleural effusions often experience dramatic and immediate relief from dyspnea after therapeutic thoracentesis. Although this is a well-recognized phenomenon, the physiologic basis for such relief remains poorly understood. Primary physiologic basis for the relief in dyspnea after thoracentesis may include the improvement of the heart and lung function. In some cases the improvement in breathlessness cannot be attributed to the improvement of gas exchange, due to the atelectatic lung(not fully expansion of the lung). Transthoracic echocardiogram (TTE) is a non-invasive, real-time viewing of the internal parts of the heart using ultrasound, which can get highly accurate and quick assessment of the various heart images, though which doctors can quickly assess a patient's heart valves and degree of heart muscle contraction.

Inclusion Criteria:

1. the estimated amount of effusion is above 500 ml;
2. Drainage was not performed within 1 month before admission;
3. assigned informed consent.

Exclusion Criteria:

1. physical weakness which is difficult to withstand the thoracentesis;
2. the happening of serious pleural reaction or reexpansion pulmonary edema on previous thoracentesis;
3. allergy to the anesthetic;
4. coagulation dysfunction, severe bleeding tendency;
5. serious mental illness who do not cooperate;
6. suspected with pleural hydatid disease;
7. skin infection around supine positioning;
8. severe heart function insufficiency who cannot lay on the back;
9. for a variety of reasons that cannot accept regular follow-up;
10. refused to sign the informed consent;
11. other conditions that is not suitable for the test.

The patients with unilateral or bilateral pleural effusion, with at least 500ml amount of effusion are enrolled in this study. Study population include malignant pleural effusion, tuberculosis pleural effusion, parapneumonic effusion, and a variety of causes for transudative pleural effusion.