The advantage and safety of emergency endoscopy have been already reported with so many successful cases. It is said that the influence of upper gastrointestinal endoscopy on the cardiovascular system is only transient and of not serious nature. We, however, think it necessary to publish the present report, since in the present case we have encountered a case where myocardial infarction was caused incidentally at the time of emergency endoscopy. The patient was an old man at the age of 67, and admitted to the Department of Gastroenterology, Akashi Muntipal Hospital, on January 13, 1975, 11:00 am., owing to tarry stool and severe anemia (Ht. 18%). The patient had been suffering from rheumatoid arthritis since 14 years ago, but did not receive the medication of adrenocortical hormone before the hospitalization. Hypertention was diagnosed with him 4 years ago, and since half a year ago, he also suffered from slight breast pains, though did not receive then any particular treatment. Four days prior to the admittance to the hospital, he began to feel dull pain at the epigastrium when he was hungry. The blood pressure was 110/70mmHg and the pulse, 100/min. in the initial inspection after hospitalization, but the pressure was recovered to 150/88mmHg at 3:20 pm. on the same day after saline and blood transfusion. There fore the emergency endoscopy was started 10 minutes later. Immediately after the commencement of endoscopy, the patient began to feel chest pains of non-specific anginous nature, and the examination was obliged to be suspend therefore without succeeding to find out the source of bleeding. The pain lasted for another two days, and ECG taken 24 hours after the endoscopy showed the sign of acute anteroseptal infarction with high values of WBC, ESR, SGOT and LDH. As of 2nd day of treatment, the patient began to have fever, and observing from the frequency of breast pains, changes of various measured values as well as the wave type of ECG, it was presumed that myocardial infarction had been caused incidentally during the course of endoscopy.