The patient underwent a successful percutaneous closure of the PFO with an Amplatzer device (AGA Medical; Plymouth, MN). She was well following the PFO closure and was no longer hypoxic. Four months later, she noticed increased dyspnea with exertion and when lying on her left side (functional New York Heart Association class III). She was not hypoxic on examination. A repeat transthoracic echocardiography with agitated saline was negative for intraatrial shunt. Pulmonary venous flows in the right lateral decubitus position were only 0.7 m/s (normal 0.4 to 0.7 m/s), suggesting no pulmonary vein stenosis. In the left lateral decubitus position, pulmonary vein flow velocities increased to 1.4 m/s (Fig 2A), with right ventricular systolic pressures increasing by 4 mm Hg from the right decubitus position, suggesting positional pulmonary vein compression resulting in elevated pulmonary venous flows and resultant elevated pulmonary pressures and dyspnea. In the standing position, her pulmonary vein flow increased further to 1.9 m/s with right ventricular systolic pressure increasing by 6 mm Hg from the right position, indicating increased pulmonary vein obstruction in the standing position, reflecting increased symptoms with standing. Pulmonary function tests demonstrated an FVC of 1.77 L (45% predicted), FEV1 of 1.49 L (47% predicted), and an FEV1/FVC of 84%, and a bronchoscopic examination confirmed the absence of bronchial obstruction.