Pulmonary hypertension (PH) may be the result of many different pathological processes. PH is a rare but recognized vascular complication following major lung resection. We describe the diagnosis and management of moderate PH resulting more than 50 years in a patient who underwent a total unilateral pneumonectomy in infancy. Unfortunately, patients who undergo pneumonectomy will likely go on to develop PH and their functional status will be greatly impacted. In the case presented, we report on a patient whose PH and symptoms improved following off-label WHO group 1 treatment.