This chest X ray demonstrates a pericardial cyst. 
	This PA view shows apparent 
 prominence of the right heart border.  Careful inspection shows a smooth, round, soft tissue density distinct from and adjacent to the right heart border.  The typical appearance of a benign pericardial cyst.
	
This lateral view demonstrates the 
 pericardial cyst   as well. It appears as a double density over the heart shadow.