Obstructive shock is often associated with poor right ventricular (RV) output and requires rapid obstruction release. A 54-year-old man was brought to our emergency department, presenting with shock. He had previously undergone esophagectomy with gastric interposition through the retrosternal route, after which he could not eat solid foods. After eating a ball of rice, he became critically ill, with a significantly increased lactate level, an indicator of shock. Though initial examinations showed no abnormalities, he was hospitalized for observation. The following day, he experienced similar discomfort while in the supine position, an hour after breakfast. Cardiac sonography revealed that the RV was remarkably compressed by a massively expanded gastric tube, causing diastolic dysfunction. After propping him into a sitting position, he recovered from shock. Upon a second examination of CT images, we recognized the massively dilated gastric tube compressing the RV. Anatomically, the retrosternal route is located directly in front of the RV. Thus, it is thought that the massively dilated gastric tube externally compressed the RV, preventing adequate RV filling and causing the obstructive shock. In such cases, the patient's position should be changed immediately to release the RV compression.