摘要Cystic tumour of the atrioventricular node is a rare primary cardiac tumour that can cause complete heart block and sudden death.Here,we describe a male case aged 42 years who suddenly died without a medical and family history of cardiac illnesses.After detailed macroscopic and microscopic examinations,a cystic mass was found in the atrioventricular nodal region.The small lesion was less than 1 cm in diameter,and consisted of small and large cystic spaces and tubular structures lined by flat,cuboidal or squamous epithelium.Immunohistochemical staining revealed the tumour epithelium positive for epithelial membrane antigen,carcinoembryonic antigen,antigen epitopes AE1/AE3,cytokeratins CK5/6 and CK7,but negative for calretinin,HBME-1,Wilms' tumor 1,factor Ⅷ,chromogranin,synaptophysin or smooth muscle actin,suggesting an endodermal rather than mesothelial origin.