A 49-year-old man with mitral regurgitation developed chylopericardium after mitral valve replacement. On postoperative day (POD) 1, the patient was started on a regular diet. On POD 2, drainage from retrosternal and intrapericardial tubes increased, becoming turbid and milky. Because the triglyceride concentration was high at 197 mg/dl, we diagnosed the condition as chylopericardium. The patient was given nothing by mouth for 2 days and, from POD 4, received a low-fat diet, after which drainage cleared and volume decreased. The 2 drainage tubes were removed on POD 6, and he was discharged without complications on POD 18.