What causes pulmonary edema?

Pulmonary edema is a condition in which fluid leaks out of the small blood vessels into lung tissue. The most common cause of pulmonary edema is heart failure. Heart failure happens when the main chamber of the heart becomes too weak or too stiff to pump blood effectively. This leads to high pressure in the lung’s blood vessels causing fluid leak. Other causes of pulmonary edema include diffuse lung tissue damage from an infection or inflammation and high altitude sickness.