How bad is pericardial effusion (fluid around the heart) if temporary?

Pericardial effusion: Most effusions are temporarary and of no great concern as they occur in the setting of inflammation around the heart. Effusions become a problem if the fluid collection is large impeding the filling of the heart by having pressure in the pericardial space that is higher than within the heart during diastolic filling . This reduces cardiac output and can cause hypotension or tamponade.