Pneumopericardium is defined as the presence of air in the pericardial cavity. It is a rare condition in adults, usually due to trauma; it is commoner in the more exposed neonate and usually iatrogenic. The clinical presentation of chest pain and shortness of breath is associated with the pathognomonic auscultatory sign described by Bricheteau: a water-mill bruit. The diagnosis is confirmed by chest X-ray which shows the air-gap sign surrounding the cardiac silhouette. The principal differential diagnosis is a pneumomediastinum. The prognosis of pneumopericardium depends on the cause and complications of which tamponade and infection are the most serious and potentially life-threatening. The treatment of pneumopericardium is bed rest and surveillance when uncomplicated: evacuation of the air becomes necessary when complications set in.