Background: Lyme disease is a common parasitic disease that can cause varied and potentially serious manifestations. The recommendations for treating some manifestations of Lyme are based on low-quality evidence, including for myocarditis. Treatment guidelines vary and are based on very low-quality evidence. IV ceftriaxone is typically recommended until the heart block resolves. Case Presentation: We report a case of a 31-year-old male admitted to our inpatient service with syncope and bradycardia. He was diagnosed with a third-degree heart block from Lyme disease. He was started on IV ceftriaxone, and his heart block improved. He had an ongoing second-degree atrioventricular block when he requested to be discharged on oral antibiotics rather than continuing IV ceftriaxone. Our patient received four doses of ceftriaxone before discharging from the hospital. He completed 2 weeks of oral doxycycline after discharge. In a follow-up phone call, he reported complete resolution of symptoms. Conclusion: This case supports the current Infectious Disease Society of America guideline of using intravenous ceftriaxone followed by oral doxycycline after the patient has improved. It also suggests that it may be safe to shorten the period of intravenous antibiotics and hospitalization. Shortening this period would reduce expenses and be more convenient for patients. More research is needed on the duration and preferred agent for treating the complications of Lyme.

Keywords: Lyme, heart block, myocarditis, case report, doxycycline.