How is primary pulmonary hypertension (PPH) linked to Fen Phen?

Rare heart conditions have been linked to the use of the diet drug Fen Phen, and studies show a correlation between long term Fen Phen users and heart valve damage in a high percentage of people. Primary pulmonary hypertension (PPH) occurs in the blood vessels in the lungs. These complications are very hard to treat and diagnose and lead to heart failure and death in some instances.