CASE PRESENTATION: A 50 year old male with past medical history of adult onset asthma, history of unprovoked deep vein thrombosis (DVT) on Warfarin, dyslipidemia, and hypertension presented as a transfer from an outside hospital for evaluation by ophthalmology for right orbital fracture after having two syncopal episodes on the morning of hospital admission. After running 15 feet at full sprint, he began to experience sudden onset chest tightness, shortness of breath, confusion, dizziness and subsequent collapse with loss of consciousness for 1 minute. He reports similar experiences in the past where he passed out from exertion over the last 10 years. Basic laboratory findings were within normal limits (WNL). Electrocardiogram showed sinus tachycardia, incomplete right bundle branch block, and T wave inversions in anterior and inferior leads. Serial cardiac biomarkers were WNL. proBNP was 373. There was no disease on chest xray. An echocardiogram with bubble study revealed an ejection fraction of 55-60%, paradoxical septal motion, right ventricle (RV) enlargement, thickened RV wall, impaired RV function, moderate-severe PA pressures. There was no pericardial effusion or intracardiac shunt. CTA thorax revealed dilated pulmonary artery. Given a history of DVT, ventilation - perfusion (VQ) scan was performed to evaluate for chronic thromboembolic disease. The VQ scan revealed two perfusion mismatch defects in the right upper lobe and intermediate probability of pulmonary embolus. Dobutamine stress echocardiography was negative for ischemia. Cardiac catheterization showed normal coronaries, normal left ventricular systolic function with ejection fraction 60% with normal wall motion, elevated left ventricular end diastolic pressure, and severe pulmonary hypertension with mean PA pressure 52 mmHG and no response to Flolan challenge. Pulmonary function tests showed normal spirometry, lung volumes and diffusion capacity. Liver function test, HIV, vasculitis panel, cardiolipin antibodies, Factor V Leiden, prothrombin gene, and homocysteine levels were unremarkable. Management included chronic anticoagulation, supplemental oxygen of 4 L NC, and anti-hypertensives. He was referred to specialized center for thrombo-endarterectomy for chronic thromboembolic pulmonary hypertension.