An unusual case of late partial tamponade of the right atrium is reported in a patient 35 days after aortic valve replacement. Chest x-rays, echocardiograms and ECG were not helpful. The diagnosis was made by emergency bedside right heart catheterization which showed a 7 cm H2O gradient between the junction of the superior vena cava and right atrium and also a 12 cm H2O pressure difference between the femoral vein and the right atrium with a normal capillary wedge pressure. Re-thoracotomy with evacuation of blood clots and control of bleeding points improved the hemodynamics dramatically. However the patient succumbed 3 weeks later due to irreversible brain damage. This is thought to be the first report of a late partial right atrial tamponade in the English medical literature.