Mitochondrial diseases are complex and rare clinical entities that can sometimes be diagnosed by their constellation of simple clinical signs. We describe a 24-year-old insulin-dependent diabetic women who was diagnosed with complete heart block and required permanent pacemaker implantation. Astute physical examination revealed opthalmoparesis, ptosis, and pigmentary retinopathy consistent with a diagnosis of Kearns-Sayre syndrome. When a young patient presents with complete heart block, a neurologic examination including funduscopy can identify Kearns-Sayre syndrome, which has far-reaching consequence for the index patient and offspring.