Safety and Efficacy Study of RENEWAL 4 AVT

Inclusion Criteria: Indications for the device Availability for follow-up at an approved Field Following center, at the protocol defined intervals Willing and capable of undergoing a device implant and participating in all testing associated with this clinical investigation Prescribed to stable optimal pharmacologic therapy for HF Age 18 or above, or of legal age to give informed consent specific to national law Able to provide documented evidence of one or more episodes of AF/AT within 12 months of implantation NOTE: Guidant recommends anticoagulation therapy per physician discretion. Exclusion Criteria: Right bundle branch block morphology Life expectancy of less than six months due to other medical conditions Expectation of a heart transplant during the period of the study Patients with or who are likely to receive a mechanical tricuspid valve during the course of the study Have a preexisting unipolar pacemaker that will not be explanted/abandoned Have an atrial tachyarrhythmia that is permanent (i.e., does not terminate spontaneously and cannot be terminated with medical intervention) within 180 days prior to enrollment Have a known hypersensitivity to dexamethasone acetate Enrolled in any other study, including drug investigation Women that are pregnant or planning to become pregnant A Cerebral Vascular Event/ Transient Ischemic Attack within 12 months of implantation During the four weeks prior to implantation, a patient experiences an episode of AF >= 48 hours in duration and was not anticoagulated for at an adequate therapeutic level (INR >= 2.0) for the 4 weeks prior to enrollment