Coupled pacing (CP), a method for controlling ventricular rate during atrial fibrillation (AF), consists of a single electrical stimulation applied to the ventricles after each spontaneous activation. CP results in a mechanical contraction rate approximately one half the rate during AF. Paired stimulation in which two electrical stimuli are delivered to the ventricles has also been proposed as a therapy for heart failure. Although paired stimulation enhances contractility, it greatly increases energy consumption. The primary hypothesis of the present study is that CP improves cardiac function during acute AF without a similar increase in energy consumption because of the reduced rate of ventricular contractions. In a canine model, CP was applied during 4 stages: sinus rhythm, acute AF, cardiac dysfunction (CD) and atrial fibrillation in the presence of cardiac dysfunction (CD*AF). The rate of ventricular contraction decreased in all 4 stages as the result of CP. In addition, we determined the changes in external cardiac work, myocardial oxygen consumption, and myocardial efficiency in the each of 4 stages. Coupled pacing partially reversed the effects of AF and CD on external cardiac work while myocardial oxygen consumption increased only moderately. In all stages but sinus rhythm, CP increased myocardial efficiency because of the marked increases in cardiac work compared to the moderate increases in total energy consumed. Thus, this pacing therapy may be a viable therapy for patients with concurrent atrial fibrillation and heart failure.