A three-year-old Appaloosa mare presents with a four-week history of exercise intolerance and recent epistaxis after exercise.

An irregular heart rhythm is auscultated during physical examination. No cardiac murmurs are ausculted and her lungs auscult clear.

An electrocardiogram (ECG) from this patient is shown in the following image.

Which one of the following choices is the correct treatment?

100.7 F (38.1 C)99.0–100.6 (37.2–38.1 C)
HR=32 bpm28-40 bpm
BR=12 brpm10-14 brpm