An implantable cardiac stimulation device and method provide electrical stimulation therapy to stabilize the ventricular rate of a heart during episodes of atrial fibrillation. The stimulation therapy may be a plurality of stimulation pulses delivered to the AV node during the AV node refractory period following the sensing of an atrial event. Alternatively, the stimulation therapy may be a plurality of sub-threshold stimulation pulses delivered to capture AV node vagal innervations following the detection of atrial fibrillation.
