collection of a bloody fluid in the pleural cavity, between the membrane lining the thoracic cage and the membrane covering the lung. Hemothorax may result from injury or surgery, especially when there has been damage to the larger blood vessels (blood vessel) of the chest wall. Other disorders that cause hemothorax include pulmonary embolism and certain tumours (tumour). If hemothorax interferes with breathing, a tube is inserted through the chest wall into the pleural space to drain the blood. Continued bleeding through the tube necessitates surgical exploration.

If both air and blood are present in the pleural cavity, the condition is called hemopneumothorax. This condition generally is caused by a penetrating chest wound or occasionally by rupture of the lung or esophagus. Surgical exploration is often required.