We describe 2 patients who presented with symptoms and clinical evidence of pulmonary hypertension. The first patient, who had severe pulmonary hypertension, underwent correction of an acquired arteriovenous (AV) fistula, which led to improvement according to clinical and noninvasive hemodynamic criteria. The second patient had severely symptomatic pulmonary hypertension associated with a large, previously unrecognized, superior mesenteric AV fistula after intra-abdominal surgery. Surgical correction of the fistula resulted in normalization of pulmonary hemodynamics assessed by right heart catheterization. Truly reversible substrates of pulmonary hypertension are rare. Acquired systemic AV fistulas are a less recognized cause of secondary pulmonary hypertension. It is unknown whether high blood flow peripheral AV shunts ultimately lead to endothelial proliferation, vascular smooth muscle hypertrophy, plexiform lesions, and other histopathologic changes that are seen in patients with left-to-right shunts due to atrial septal defects, ventricular septal defects, and patent ductus arteriosus.