Spontaneous arrhythmias in canine HF model. A, Representative ECG from Ctl and HF dog hearts. B, Representative Holter monitor recording in conscious state for HF dog showing frequent PVCs, couplets, and runs of spontaneous nonsustained VT. Insert shows close up of a 16-beat and a 4-beat run of VT. Abbreviations: control (Ctl), heart failure (HF), premature ventricular complex (PVC), ventricular tachycardia (VT).