A calcified amorphous tumor (CAT) of the heart is a rare, non-neoplastic, intracavitary cardiac mass. Histological examination reveals the presence of calcified and amorphous fibrous material with underlying chronic inflammation. Some studies have reported that CAT typically exhibits rapid growth. However, we observed a case in which CAT unexpectedly ruptured within approximately two weeks. There was no cerebral infarction or significant valvular disease, therefore we were not sure about the indication for surgery
however considering the epidemiological possibility of CAT, we decided to operate and were able to treat the patient without complications.