Following open-heart surgery, fluid may collect within the pericardium (a sac around the heart) either because the chest tube that accompanied the patient from the theatre did not drain well or due to infection, this is termed Pericardial effusion. The presence of pericardial effusion prevents contraction of the heart and can lead to a life-threatening condition called Cardiac Tamponade.
Pericardiocentesis is an invasive procedure to remove fluid from the pericardium, it relieves symptoms of pericardial effusion such as increased breathing.