A new drug called Letairis (ambrisentan) plus new guidelines are updating treatment for pulmonary arterial hypertension

Please see the August 2012 FDA warning concerning the use of Revatio in children with PAH

In pulmonary arterial hypertension, there is continuous high blood pressure in the pulmonary arteries...which carry oxygen-poor blood from the right ventricle to the lungs.

It's a rare condition that's due to tightening of pulmonary arteries...thickening of the walls of pulmonary arteries...or to blockages caused by blood clots in smaller arteries.