The right ventricle pumps blood returning from the body into the pulmonary arteries to the lungs to receive oxygen. The pressures in the lung arteries (pulmonary arteries) are normally significantly lower than the pressures in the systemic circulation. When pressure in the pulmonary circulation becomes abnormally elevated, it is referred to as pulmonary hypertension. This most commonly occurs when the pulmonary venous pressure is elevated, so called pulmonary venous hypertension (PVH). This pressure is transmitted back to the right side of the heart and the pulmonary arteries. The result is elevated pulmonary pressure throughout the pulmonary circulation. Some of this is a direct pressure transmission from the venous system backward and some can result from a reactive constriction of the pulmonary arteries.

Less commonly, pulmonary hypertension results from constriction, or stiffening, of the pulmonary arteries that supply blood to the lungs, so called pulmonary arterial hypertension (PAH). Whether it is pulmonary venous or pulmonary arterial hypertension, it becomes more difficult for the heart to pump blood forward through the lungs. This stress on the heart leads to enlargement of the right heart and eventually fluid can build up in the liver and other tissues, such as the in the legs.

Signs and symptoms of pulmonary hypertension
Many people with pulmonary hypertension may have no symptoms at all, especially if the disease is mild or in the early stages. Pulmonary hypertension symptoms may include:
-- Shortness of breath that worsens with activity
-- Other common complaints are cough, fatigue, dizziness, and lethargy.
-- With the advancement of the condition and ensuing right heart failure, shortness of breath may become worse and retention of fluid in the body may increase (due to failure of the heart to pump blood forward) resulting in swelling the legs.
-- People may also complain of chest pain and Angina.
-- Depending on the underlying associated disease, pulmonary artery hypertension can have other manifestations. For example, characteristic skin changes seen in scleroderma, or the signs of liver disease seen in portopulmonary hypertension.