A 58 year old black man presented with progressive dyspnea and persistent systemic arterial hypoxemia. Initial hemodynamic evaluation revealed mitral valve prolapse and evidence for isolated right to left shunting, presumed to be extracardiac. A detailed pulmonary evaluation disclosed normal volume and flow parameters with a mild reduction of the single breath carbon monoxide diffusing capacity. An open lung biopsy disclosed no abnormalities. Radionuclide studies of the heart, however, suggested the possibility of a filling defect in the right atrium, and echocardiography enforced the impression of a mass in the right atrium, subsequently demonstrated by superior vena cava angiography. Our report outlines the use of multiple diagnostic tools in difficult situations and stresses the importance of right atrial myxoma in the differential diagnosis of isolated right to left shunting.
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