Atrial fibrillation is the most common supraventricular arrhythmia in the dog and is most frequently observed in animals with cardiac disease associated with remodelling of the left atrium. Increased body weight is a risk factor for the development of this arrhythmia, whereas sex and age do not, differently from humans. The development of atrial fibrillation is a negative prognostic factor in dogs with myxomatous mitral valve disease and dilated cardiomyopathy associated with congestive heart failure. Treatment of canine atrial fibrillation aims at reducing the heart rate, because arrhythmia is usually long-standing persistent or permanent, and restoration of a stable sinus rhythm can be difficult
