OBJECTIVES: Sinus Node Disease (SND) is a very common indication for cardiac pacemakers. In most cases patients have dual-chamber (DDD) pacing systems implanted. Recent studies showed benefits of atrial pacing (AAI) rather than DDD. Not infrequently subsequent atrioventricular block develops and upgrade of AAI to DDD is necessary, what creates additional costs. The aim: to compare costs of primary DDD pacemaker implantation to primary AAI implantation, in patients without initial DDD indications. METHODS: The cost comparison analysis was based on deterministic model in the time window of 10 years. Model assumptions: pacemaker battery longevity: AAI - 8 y.; DDD - 6 y. The rate of upgrade necessity was taken from the observation of 752 SND patients who had AAI implanted between 1993 and 1997. Records of patients were examined to find cases requiring further upgrade procedure. The rate of upgrade to DDD was 19.1% within a mean observational period 7.4 years. Perspective: public health care payer. Linear costs depreciation; 5% discount rate. Sensitivity analysis: for upgrade to DDD rate and procedure costs. RESULTS: Projected to 10 years rate of upgrade was 25.8%. Cost of primary DDD approach was $4719 PPP; primary AAI approach - $3804 PPP; cost of hypothetical (ideal) approach in which all patients that would need upgrade in the future were identified before implantation was $3505 PPP. Primary DDD would become equal to primary AAI strategy if upgrade rate was 56% or more. The lower relative DDD costs the lower was the equality upgrade rate, and the higher absolute differences the more beneficial was AAI strategy. CONCLUSIONS: Implantation of AAI PM in SND patients without DDD indications is cost saving comparing to DDD in every patient. Better identification of patients who will need upgrade to DDD may bring additional savings.