Pleural effusion is the state of having excess fluid in pleural cavity (the space surrounding the lungs). Although there is normally some fluid in this space, to much can cause difficulty breathing. There are four different types of fluid that fill the pleural cavity. There are many different causes including, left ventricular failure, pulmonary embolism, and cirrhosis, bacterial pneumonia, cancer, viral infection, and pulmonary embolism. The underlying cause determines the course of the infection.