A 76-year-old female presented with a large hiatus hernia with intrathoracic stomach manifesting as severe exertion dyspnea. She had no cardiac or pulmonary disease, and neither anemia nor cyanosis, but respiratory function was mildly impaired. Chest roentogenography showed a large abnormal shadow overlapping the lower half of the heart. Transthoracic echocardiography demonstrated a mass compressing the left atrium and extending to the posterior part of the left ventricle, but the actual cause of the mass was not clear. Cross-sectional spiral computed tomography(CT) revealed a large hiatus hernia with intrathoracic stomach located just behind the left atrium with resultant mild anterior shift of the whole heart. Moreover, three-dimensional curved reformation CT suggested that the intrathoracic stomach was located in the upside-down position, which was confirmed by subsequent gastroesophagography. She experienced gradual progression of exertion dyspnea during the following 3 months. Follow-up CT revealed no significant increase of left atrial compression, but subsequent spirometric study showed increased impairment of respiratory function. Surgical repair for the hiatus hernia was successfully performed, and eventually achieved resolution of the symptoms. The cause of exertion dyspnea was probably cardiac compression and impaired respiratory function. The therapeutic strategy of surgical repair is recommended in elderly patients with hiatus hernia complicated with cardiac compression and respiratory impairment.