The Auenbrugger sign occurs during a large pericardial effusion when an epigastric bulge is present. This represents the large pericardial effusion extending subxiphoid. Compression of this bulge may cause hemodynamic compromise and cardiac tamponade. Below is a chest x-ray of a pericardial effusion. The cardiac enlargement is called a "water bottle heart". This image helps demonstrate the proximity of the pericardial fluid to the mid-epigastic area where it may buldge to cause the Auenbrugger sign.