At my 20 week ultrasound they found fluid around the baby's heart? what does this mean?

Fetal pericarditis: The fluid around the heard called "pericarditis". Isolated findings means probably nothing. "pericardial fluid 2 mm or greater in thickness may be associated with structural anomalies or hydrops, but its clinical significance in the absence of these associated findings has not been evaluated". Reference: http://www.Jultrasoundmed.Org/content/13/4/291.Abstract.