Laboratory testing was negative for HIV, autoimmune diseases, hepatitis, and hypercoagulability. Pulmonary function was normal, and 6-min walk distance was 664 m. Transthoracic echocardiogram demonstrated normal left ventricle size and function, a mildly dilated right ventricle with preserved systolic function (right ventricular fractional area change of 39%, tricuspid annular plane systolic excursion of 2.0 cm), severe tricuspid regurgitation, estimated right ventricular systolic pressure of 83 mm Hg, right atrial pressure of 15 mm Hg, and positive bubble study for late targets suggesting an extracardiac shunt. Chest CT scan showed two small pulmonary arteriovenous malformations (AVMs) (Fig 1), and an MRI of the liver demonstrated multiple small AVMs. Right-sided heart catheterization showed a mean right atrial pressure of 9 mm Hg, mean pulmonary arterial pressure of 35 mm Hg, pulmonary capillary wedge pressure of 12 mm Hg, cardiac output of 3.5 L/min, pulmonary vascular resistance of 5.8 Wood units, and lack of vasoreactivity. Wedge angiography demonstrated rapidly tapering vessels and an absence of capillary blush without visible AVMs in the injected pulmonary arteries (Fig 2).