The number of heart transplantations performed in Japan has been continuously increasing. Here, we report the case of a patient with an unruptured cerebral artery aneurysm after undergoing heart transplantation and was treated using coil embolization. The patient was a 50-year-old woman who was positive for heparin-induced thrombocytopenia (HIT) antibodies and underwent heart transplantation for dilated cardiomyopathy. An unruptured middle cerebral artery aneurysm was treated with coil embolization using argatroban as a heparin substitute. The patient was discharged without any complications. Despite these patients with heart transplantation are characterized by high HIT antibodies rate and the need for immunosuppressive agents, they currently have an excellent prognosis, especially in Japan. Therefore, the knowledge of patient characteristics after heart transplantation is essential for ensuring that these patients receive the most appropriate treatment.