Three-lead ECG from a Doberman pinscher with dilated cardiomyopathy. There is uncontrolled atrial fibrillation. The fast heart rate, lack of discernible P waves, and irregularity are all characteristic of atrial fibrillation. In this patient, the QRS complexes are wide because of left ventricular enlargement. Because of heart orientation in deep-chested animals (eg, Doberman pinschers), left ventricular enlargement often creates a widened QRS complex (instead of a tall R wave). Heart rate ranges from 230300 bpm (paper speed, 50 mm/sec; sensitivity, 10 mm/mV).
