At initial presentation, heart rate ranged from 180 to
300 beats/min (median, 200 beats/min). Heart rate was
obtained from the ECG by evaluating the number of
complexes in a 6-second period. At first re-evaluation
after initiating amiodarone therapy, 6 dogs were in
a sinus rhythm with median heart rate of 105 beats/min
(range, 100–120 beats/min). In the 11 remaining dogs,
heart rate ranged from 120 to 200 beats/min (median,
160 beats/min). In 13 dogs, heart rate decreased by more
than 20% (range, 20–50%), corresponding to a median
decrease from initial heart rate that ranged from 40 to
120 beats/min (median, 100 beats/min). Five of these
dogs were solely receiving amiodarone therapy. Heart
rate remained unchanged in 4 dogs who continued to be
in AF