Lungs (IMAGE) Max-Planck-Gesellschaft Caption Excessive cell proliferation in the blood vessel walls of the pulmonary circulation leads to an obstruction in the blood flow, so that the vessels can pump less and less blood. The pressure in the blood vessel increases, and the heart must pump harder to transport blood to the lungs. Credit Max Planck Institute for Heart and Lung Research Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.