Background: Heart Rate Score (HRSc), the percent of all atrial paced and sensed event in the largest 10 bpm rate histogram bin of a pacemaker, predicts survival in patients with cardiac devices. No correlation between HRSc and development of atrial fibrillation (AF) has been reported. Objective: To evaluate the relationship between pacemaker post-implantation HRSc and newly-developed AF incidence. Methods: Patients with dual-chamber pacemakers, implanted 2013-2017, with ALTITIUDE remote monitoring data with {greater than or equal to}600,000 beats of histogram data collected at baseline were included (N=34,543). HRSc was determined from the post-implantation histogram data during the initial 3 months. Patients were excluded if they had AF, defined as atrial high-rate episodes >5 minutes or >1% of right atrial beats >170 bpm during the initial 3-months post-implantation. New AF, after the baseline period, was defined by each of the following: >1%, >10% or >25% of atrial beats >170 bpm or Atrial Tachycardia Response (ATR) events >24 hr. Results: Patients were followed a median of 2.8 (1.0-4.0) years. Patients with initial HRSc{greater than or equal to}70% were older, had higher %RA pacing, had lower %RV pacing and were more likely programmed with rate-response vs subjects with HRSc<70%. The incidence of AF increased in proportion to HRSc (Log-Rank P-value <0.001); results were insensitive to AF definition. Initial HRSc (HR:1.07, 95% CI:1.05-1.09; P<0.0001) independently predicted AF after adjusting for age, gender, % RV pacing and rate-response programming. The %RA pacing and initial HRSc correlated. Conclusion: HRSc predicts subsequent AF independent of well-known risk factors in pacemaker patients.