Chylopericardium after an intrapericardial procedure is rare, and satisfactory explanations of its possible causes are lacking.Herein, we present 4 cases of chylopericardium that developed after intrapericardial surgery, and we review the literature. Our literature review revealed 29 cases of chylopericardium that complicated intrapericardial operations, to which we added our 4 cases for analysis. The 33 surgical procedures involved repair for congenital heart disease (n=21), valve surgery (n=5), coronary artery bypass grafting (n=6), and other (n=1). Causes were verified in 7 patients: small lymphatic injury in 3 and high venous pressure or venous thrombosis in 4. Of the 26 patients with chylopericardium of unknown origin, 15 had congenital heart disease. Ten of these 15 had chromosomal abnormalities, especially trisomy 21 (Down syndrome); these patients typically had increased lymphatic permeability, which raised the likelihood of chylopericardium. Five revascularizations for coronary artery disease required harvesting of the left internal thoracic artery for reconstruction, incurring a risk of damage to the drainage site of the right efferent lymphatic trunk. In addition, all 26 patients with chylopericardium of unknown origin underwent dissection of the ascending aorta and the main pulmonary artery, near the right efferent lymphatic trunk. Inadvertent injury to the trunk during the dissection would have increased the risk of chylopericardium. Accordingly, even though the overall incidence of chylopericardium during intrapericardial procedures is low, we recommend a meticulous dissection of the ascending aorta from the main pulmonary artery.