['Recent studies have demonstrated that ventricular rate control is a viable treatment strategy for patients in atrial fibrillation (AF). The purpose of this study was to determine whether or not the benefits of coupled pacing (ie, a proposed rate control therapy) could be used during persistent AF.', 'Six mongrel dogs were chronically implanted with endocardial atrial and ventricular pacemaker leads and two standard dual-chamber pacemakers. With the use of two custom "Y"-lead adapters, the pacemakers were used to induce AF and to apply coupled pacing. Left ventricular end-diastolic and systolic volumes were measured by echocardiography to determine ejection fractions.', 'Persistent AF significantly increased both ventricular rate and left ventricular dimensions. After sustained coupled pacing had been applied for 3 to 4 weeks, left ventricular volumes and contractile rate were significantly reduced and returned toward the values measured prior to the induction of persistent AF. Coupled pacing increased the ejection fraction that had been reduced by persistent AF.'] Does coupled pacing reverse the effects of persistent atrial fibrillation on the left ventricle?