CASE PRESENTATION: A 20 year old female with a history of diabetes mellitus, hypertension, and end-stage renal disease on hemodialysis presented with a two month history of severe exertional dyspnea. On exam her O2 saturation was 99%. Her neck was without jugular venous distention. She was in no respiratory distress but did have lower lobe rales and an S3 gallop. She had a left arm AV fistula, and trace bilateral lower extremity edema. Her pulmonary function testing and CT chest PE protocol were negative. A recent echocardiogram was normal and without valvular disease or pulmonary hypertension. She had a normal ventilation-perfusion scan, normal arterial blood gas, and did not desaturate with ambulation. Her symptoms were not relieved by bronchodilators and were worsened by fluid removal via dialysis. Attention then shifted to her AV fistula. A fistulogram showed a flow of 1500cc/min, making the fistula the prime suspect for etiology of her symptoms. A repeat chest x-ray revealed pulmonary vascular congestion. Repeat echocardiogram now showed a severe dilated cardiomyopathy with an ejection fraction (LVEF) of 25% and a mean pulmonary artery systolic pressure (mPAP) of 46 mmHg without evidence of intracardiac or pulmonary shunt. Cardiac catheterization showed a cardiac output (CO) of 5.7 L/min, a pulmonary capillary wedge pressure (PCWP) of 36 mmHg, and pulmonary hypertension with a mPAP of 43 mmHg. Her fistula was then banded from 1500cc/min to 900cc/min and further to 590cc/min as her symptoms were persisted after the first banding - though her LVEF had improved to 55%. Of note, her mPAP improved to 38mmHg and then further to 18mmHg (with a CO of 5.0 L/min) with the second banding. It was at this point that the patient experienced complete symptomatic relief.