Eisenmenger (I-sun-meng-uhr) syndrome is a long-term complication of an unrepaired heart defect that someone was born with (congenital).
The congenital heart defects associated with Eisenmenger syndrome cause blood to circulate abnormally in your heart and lungs. When blood doesn't flow normally, the blood vessels in your lungs become stiff and narrow, increasing the pressure in your lungs' arteries (pulmonary arterial hypertension). This permanently damages the blood vessels in your lungs.
With early diagnosis and repair of congenital heart defects, this life-threatening condition can usually be avoided. If Eisenmenger syndrome does develop, it requires careful medical monitoring. Medications can improve symptoms and prognosis.