Pulmonary congestion usually occurs in left-sided heart failure; when the left ventricle cannot effectively pump blood out of the ventricle into the aorta and to the systemic circulation. Blood volume and pressure in the left atrium increases which decreases blood flow from the pulmonary vessels. Pulmonary venous blood volume and pressure increase, forcing fluid from the pulmonary capillaries into the pulmonary tissues and alveoli, causing pulmonary interstitial edema and impaired gas exchange.
