Thyroid hormones(TH), one of the human′s essential hormones, play a crucial role in the cardiovascular system.Studies have shown that hypothermia, blood dilution, vascular endothelial injury, ischemia-reperfusion, and inflammatory factor release during cardiopulmonary bypass may cause thyroid dysfunction, leading to the euthyroid sick syndrome(ESS). There is a close correlation between ESS and postoperative low cardiac output and elevated systemic vascular resistance, which seriously affects the prognosis of pediatric patients.Studies have shown that perioperative supplementation of thyroid hormones can reduce ESS levels, especially among pediatric patients and those children with complex congenital heart disease have apparent clinical advantages.However, the results from different clinical studies varied, and currently, thyroid hormone replacement therapy is under debate.This review examines the available literature on the clinical effects of thyroid hormone on the cardiovascular system and the relationship between ESS and cardiopulmonary bypass.The clinical evidence of the treatment of ESS is gathered and discussed with an intent to find a gap for further research.