Inclusion Criteria:

Patients who meet the following criteria should be given consideration for inclusion in the clinical investigation:

• Meet all device indications and contraindications
• Willing and capable of providing informed consent, undergoing a device implant, participating in all testing associated with this clinical investigation at an approved clinical investigational center and at the intervals defined by this protocol
• Prescribed to stable optimal pharmacologic therapy for heart failure
• Creatinine < 2.5 mg/dL obtained no more than two weeks prior to enrollment
• Age 18 or above, or of legal age to give informed consent specific to state and national law
• Geographically stable residents who are available for follow-up
• 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:

Patients who will be excluded from the investigation are those who meet any one of the following criteria:

• Have a preexisting non-Guidant left ventricular lead
• Have a preexisting unipolar pacemaker that will not be explanted/abandoned
• Documented life expectancy of less than six months or expected to undergo heart transplant within the next six months
• 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 a 0.7 mg dose of dexamethasone acetate
• Have surgically uncorrected primary valvular heart disease
• Currently requiring hemo-dialysis
• Have had a myocardial infarct, unstable angina, percutaneous coronary intervention, or coronary artery bypass graft during the preceding 30 days prior to enrollment
• Have hypertrophic obstructive cardiomyopathy or infiltrative cardiomyopathy (e.g., amyloidosis, sarcoidosis)
• Have a mechanical tricuspid heart valve
• Enrolled in any concurrent study, without Guidant written approval, that may confound the results of this study
• 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 ³ 48 hours in duration and was not anticoagulated at an adequate therapeutic level for the 4 weeks prior to enrollment with an INR = 2.0-3.0 at enrollment
• Women who are pregnant or plan to become pregnant

Note: Women of childbearing potential must have a negative pregnancy test within 7 days of enrollment