Eisenmenger syndrome (ES), the most advanced form of pulmonary arterial hypertension (PAH) associated with congenital heart disease, is a devastating condition that has a considerable impact on patients' lives. Patients who develop ES typically exhibit 1 or more of a range of cardiac defects, including ventricular septal defects, atrial septal defects, and patent ductus arteriosus. The nature of the congenital defect underlying ES is important because it has prognostic implications. Although ES shares similar morphological findings with idiopathic PAH, clinical differences exist between the 2 etiologies. Adults with ES exhibit increased survival and more favorable hemodynamics than those with idiopathic PAH. Treatment options for patients with ES have historically been limited; however, recent successes have been achieved with the use of therapies targeted against the pathophysiological pathways that underlie PAH. The dual endothelin receptor antagonist bosentan was demonstrated to improve hemodynamics and exercise capacity without compromising oxygen saturation, both in the short and long term. Improvements in hemodynamics also have been observed with the single endothelin receptor antagonist sitaxsentan. The phosphodiesterase type V inhibitor sildenafil may improve functional class, oxygen saturation, and hemodynamics in patients with ES, and beneficial effects of prostacyclin and prostacyclin analogs in patients with ES have been reported. The treatment of patients with PAH with the use of combinations of targeted therapies is becoming increasingly commonplace and may offer an alternative option for treatment of patients with ES. The authors of future studies may seek to investigate whether the pulmonary vascular remodeling in ES can be targeted and reversed.