A 5 year old 9 month pregnant Suffolk Punch mare presented for mild colic and fever of unknown origin. The mare was diagnosed with fibrinous pericarditis and severe secondary pre-renal azotemia. The mare was managed medically with pericardiocentesis, pericardial lavage and supportive care. The mare responsed to these treatments but no definitive etiology was identified. Cardiology recheck approximately 4 weeks later was normal.