X-ray chest PA view illustrating air fluid level in the pericardial cavity. In the yesteryears, air used to deliberately introduced into the pericardial cavity after partial aspiration of pericardial fluid to visualise intra pericardial structures by their contour and to assess the pericardial thickening. Now a days, with the availability of multiple imaging modalities like echocardiography, CT scanning and MRI scanning, it is seldom necessary. Hydropneumopericardium can occur if an esophageal malignancy invades the pericardial cavity and produces an oesphageopericaridal fistula. In such case hydropneumopericardium is rapidly converted into a pyo pneumopericardium.