The Chiari network is an embryological remnant. It has rarely clinical importance but may very infrequently cause thrombosis and some other complications. Chest pain and pulmonary thrombosis were developed in a 23-year-old man. Cardiac ultrasonography revealed Chiari network in his right atrium, and no other thrombogenic lesions were found. Although anti-coagulant therapy was performed, pulmonary thrombosis were redeveloped. Chiari network was thought the cause of chest pain and pulmonary thrombosis. Operative removal of Chiari networks performed. The patient was postoperatively free from chest pain and pulmonary thrombosis.