The pleural cavity also known as the pleural space, is the thin fluid-filled space between the two pulmonary pleurae (known as visceral and parietal) of each lung. A pleura is a serous membrane which folds back onto itself to form a two-layered membranous pleural sac. The outer pleura (parietal pleura) is attached to the chest wall, but is separated from it by the endothoracic fascia.

The inner pleura (visceral pleura) covers the lungs and adjoining structures, including blood vessels, bronchi and nerves. The pleural cavity can be viewed as a potential space because the two pleurae adhere to each other (through the thin film of serous fluid) under all normal conditions.

The pleural cavity, with its associated pleurae, aids optimal functioning of the lungs during breathing. The pleural cavity also contains pleural fluid, which acts as a lubricant and allows the pleurae to slide effortlessly against each other during respiratory movements.

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