Between June 1983 and September 1984, 3 patients operated for mitral valve disease presented with acute right heart failure due to right atrial compression. Emergency echocardiography did not show pericardial separation around the ventricles but in the apical 4 chamber view severe right atrial compression by an extracardiac mass was observed. Emergency surgery was performed in all three cases to evacuate a localised haemopericardium despite the absence of pericardial fusion. These cases of acute right ventricular failure underline the importance of multiplying the number of echocardiographic views in order to detect localised pericardial effusion. The diagnosis should be made as soon as possible as clinical deterioration may be rapid despite effusions of small volume. The main differential diagnoses are right atrial thrombosis and acute postoperative pulmonary embolism. In these cases of localised tamponade, the clinical signs are the result of vena caval compression or extrinsic compression of the tricuspid orifice. The preferential localisation of the haemopericardium around the right atrium is difficult to explain. It is probably related to the low pressures in this region. The echocardiographic appearances of this condition have been established allowing reliable diagnosis.