A patient with rheumatic mitral valve disease and persistently elevated jugular venous pressure (JVP) is described. Angiography revealed a valve-like structure in the superior vena cava (SVC) at the site where a pressure gradient was recorded. At operation, this previously unreported anomaly proved to have been caused by aneurysmal dilatation of the left atrium which exerted traction on the pericardial insertion to the SVC. Disinsertion of the pericardial attachment to the vena cava at the time of mitral valve replacement released the compression. Postoperatively, the JVP became normal.