Para-sternal echocardiography proved impossible in a case of a large pneumopericardium caused by an oesophageo-pericardial fistula. However, M mode and sector scanning showed separation of the pericardium, giving non-homogeneous echoes, and shaded echographic areas caused by the interference of air which masked all recognisable structures. This occurred in time with systole, a sign which we associate with the pneumopericardium itself.