The pneumopericardium represents as a pneumatic pericardium tamponade an acute emergency situation. It belongs to the most dangerous kinds of extra-alveolar air and only the immediate punction prevents the deleterious results of the low output syndrome. Under mechanical ventilation three preterm infants with respiratory distress syndrome developed a pneumopericardium. All these patients had got other kinds of extra-alveolar air before. Acute cardiac shock with hypoxemia, bradycardia and systemic hypotension refer to the presence of a pneumopericardium. The proof of these symptoms justifies the immediate punction and, if its positive, the supply with a siphon drainage. Requirement to an early diagnosis of pneumopericardium is a thorough monitoring of the tc pO2, tc pCO2 and paO2, of systemic blood pressure, monitoring in the aorta or in the radial artery, of central venous pressure and self-evident the control of heart and breathing.