An 11 year old spayed female German Shepherd Dog presented to the Cornell University Hospital for Animals (CUHA) Cardiology Service with third degree heart block. The patient initially presented to her primary veterinarian for a routine dental cleaning during which ECG monitoring revealed the abnormality. She then progressed to intermittent syncopal episodes of increasing frequency after which her owners decided to pursue pacemaker implantation as definitive treatment. The pacemaker was placed but post-operative complications led to incomplete capture. As a result, a second pacemaker was placed on the contralateral side. This paper will discuss the etiology, presentation, diagnosis, treatment, and clinical anatomy of third degree heart block in dogs.