Haemothorax is a medical condition that occurs when blood accumulates in the pleural cavity, which is the space between the lung and the chest wall. Some synonyms for haemothorax include pleural bleed, hematopleural effusion, blood in the chest, or a bloody chest. Haemothorax is typically the result of an injury or trauma to the chest wall, such as a car accident or a punctured lung. The condition can be life-threatening and requires immediate medical attention. Treatment usually involves draining the blood from the pleural cavity and addressing any underlying injuries to prevent recurrence. If left untreated, haemothorax can lead to lung collapse, pneumonia, and other serious complications.