BackgroundFirst-degree atrioventricular block (AVB) may lead to complete AVB. Herein, we present a case of a complete AVB under thoracic epidural catheter infusion of ropivacaine with fentanyl in a patient with first-degree AVB and myasthenia gravis.Case presentationA 74-year-old woman with first-degree AVB underwent thymectomy for myasthenia gravis. Continuous thoracic epidural catheter infusion of 0.2% ropivacaine with fentanyl was initiated at 15 min before the end of the surgery. At 9 h postoperatively, the electrocardiogram showed a 10-s-long pause due to complete AVB. Thus, a temporary pacemaker was implanted, and at 19 h postoperatively on postoperative day 1, cardiac pacing was initiated and lasted approximately 30 s. After catheter removal, she had no further episodes of complete AVB.ConclusionFirst-degree AVB may lead to complete AVB under the influence of thoracic epidural infusion of ropivacaine in patients with myasthenia gravis.