We describe a case of an intracardiac foreign body that was treated by surgery. A 27-year-old man sustained a neck injury by a nail fired from a pneumatic nail gun, and was admitted to a hospital. Chest radiography did not show any abnormality, and his injury healed after 1week. A radiography performed during a routine medical checkup after 2 months indicated that a nail was located within the heart. He was subsequently admitted to our hospital for further examinations. Chest computed tomography CT revealed the presence of a nail-like foreign body in the right ventricle. We diagnosed the patient with an intracardiac foreign body that was related to the injury sustained 2 months previously, although the underlying mechanism was unknown. He underwent emergency surgery, and the foreign body was removed under cardiopulmonary bypass without any complications. When a rigid substance impacts the body at high speeds, we should consider that some fragments could remain embedded in the body. CT scans are very useful for the diagnosis and identification of foreign bodies.