1. any situation in which atria and ventricles are activated and contract independently, as in complete A-V block;
2. more specifically, the dissociation between atria and ventricles that results from slowing of the atrial pacemaker or acceleration of the ventricular pacemaker at nearly equal (rarely equal) rates, each depolarizing its own chamber, thus interfering with depolarization by the other (interference-dissociation).