During a mitral valve replacement surgery in a girl of 22 years of age, it was accidentally discovered that the valve was destroyed due to a tumor and the histopathology and immunohistochemistry findings have proved it to be undifferentiated sarcoma. She was advised by the surgeon to go for chemotherapy. There was a delay of three months from the side of the patient to reach us and during that interval she has developed secondaries in the brain. This case is being presented here for its rarity.