It is a chronic condition which affects those blood vessels which are related to lungs or from the lungs. Causes of pulmonary vascular diseases are varies according to lung’s blood vessels are affected. The definition of pulmonary vascular disease is simple: any condition that affects the blood vessels along the route between the heart and lungs. Blood travels from the heart, to the lungs, and back to the heart. This process continually refills the blood with oxygen, and lets carbon dioxide be exhaled.