Lungs gave normal results; no murmur was audible over the lower left lung. The remainder of the examination revealed no abnormalities; clubbing of fingers and toes was not evident. Fluoroscopic examination of the chest revealed a rounded mass 6 cm. in diameter near the posterolateral aspect of the heart. The mass pulsated, but whether the pulsation was transmitted from the heart or whether the mass itself was pulsating could not be determined with certainty. When the patient executed the Valsalva maneuver, the mass diminished in size. The lung fields were otherwise clear, and the cardiac silhouette was normal in size and contour. Laboratory studies showed that the hemoglobin was 13.6 gm. per 100 cc. and the hematocrit 48%. The arterial oxygen saturation was 84.9%; this rose to 94.3% after breathing of 100% oxygen for 30 minutes. There was no dyspnea after four minutes of treadmill exercise, although the arterial oxygen