Blood cysts are benign tumors in nature and seldom need surgical removal. Herein, we report an 86-year-old patient with a blood cyst originating from the fossa ovalis accompanied by an atrial septal defect. The patient used the bizarre sleeping postures, including prostrating and worshiping, to relieve chest tightness. The septal base defect kept the tumor progressively enlarged with time, which contributed to a "ball-valve "effect and caused tricuspid flow obstruction. It was resolved after excision. This case report emphasizes that long-term follow-up and increased awareness are required for unpredictable intracardiac blood cyst development.
Keywords: Atrial septal defect; Intracardiac blood cyst; Tricuspid obstruction.