CASE PRESENTATION: A 50-year old female non-smoker presented with shortness of breath for the past 1 year. Pertinent past history included HHT with pulmonary arteriovenous malformation (AVM), status post coil embolization of her pulmonary AVM 3 years ago. Computed tomography imaging of the thorax did not show new AVM or recanalization of previously embolized AVM. Pulmonary function tests were normal. Cardiopulmonary exercise test showed reduced exercise capacity, anaerobic threshold, oxygen pulse, VE/MVV and increased VE/CO2, with no ventilatory abnormality observed. She was evaluated with transthoracic echocardiogram which showed a pulmonary artery systolic pressure of 64mmHg. Transesophageal echocardiogram showed normal valvular function and intact interatrial and interventricular septum. Diagnostic right heart catheterization study demonstrated pulmonary capillary wedge pressure of 8mm Hg, cardiac output of 4.1L/min and mean pulmonary arterial pressure of 64mmHg. There was no step up in oxygenation from the inferior venous cava to the pulmonary artery to suggest intra-cardiac shunt. Pulmonary vascular resistance was markedly elevated at 11 Woods, suggesting pulmonary arterial hypertension (PAH) as the cause of PH.