A 54-year-old man developed transient cardiac arrest due to malignant hyperthermia (MH) during clipping of a cerebral aneurysm. He was found to have unruptured middle cerebral artery aneurysms on both sides. At the first operation, on the left aneurysm, anesthesia was induced by thiopental and vecronium and maintained by isoflurane, nitrous oxide and oxygen. He suddenly developed cardiac arrest soon after an arrythmia of grade 3 A-V block which occurred 6.5 hours after the operation had started. Fortunately the heart recovered after 20 minutes of cardiopulmonary resuscitation. After this accident, the rectal temperature rose to 41.5°C with the manifestation of macro hematuria, metabolic acidosis, and elevation of the levels of serum enzymes GOT, LDH, and CPK. At this point, we suspected MH. Five weeks after the first operation, the second operation, on the right aneurysm was performed. Before anesthesia, dantrolene sodium was administered and a percutaneous pacemaker was inserted intravenously. Balance anesthesia was induced and the second operation was completed uneventfully. We should keep in mind that dantrolene should always be prepared and injected immediately under general anesthesia whenever MH is suspected.