An apparatus and method is presented for treating patients with sinus node dysfunction who have apparently normal intrinsic AV conduction and thus do not require ventricular pacing unless there is an unexpected AV conduction failure. In one embodiment, a cardiac device with dual-chamber pacing capability is programmed to operate in a primary DDI (or DDI(R)) mode adjusted to pace only the atria if intrinsic AV conduction is intact and switch to a secondary DDD (or DDD(R)) mode upon detection of AV block.