AIMS: Sedentary time (ST) can be reduced in patients with coronary artery disease (CAD) during cardiac rehabilitation (CR), but most patients relapse to sedentarism within months. We examined the effectiveness of a 3-week remote booster intervention on ST changes in CAD patients. METHODS: CAD patients who previously (2.0 [1.9-2.2] years) completed CR were included in this randomized controlled trial (1:1, stratified for gender). All participants received usual care, whereas booster participants additionally received a 3-week remote behavioral change intervention. The primary outcome was the change in accelerometer-derived ST from baseline to post-intervention and secondary outcomes included changes in sedentary behaviour and physical activity (PA) characteristics. A baseline constrained linear mixed-model on an intention-to-treat basis was used. RESULTS: Participants (19% female, booster: n=21, control: n=21) were 69 [63-75] years old. Greater decreases in ST (-1.3 (95% confidence interval (CI): -2.0
-0.6) versus -0.1 (95% CI: -0.8
0.6) h/day, p-interaction=0.012) and number of prolonged sedentary bouts (-1.1 (95% CI: -1.6
-0.6) versus 0.2 (95% CI: -0.3
0.7) bouts/day, p-interaction<
0.001) in combination with larger increases in light PA (+1.1 (95% CI: +0.5
+1.8) versus +0.2 (95% CI: -0.4
+0.8) h/day, p-interaction=0.030) were found for the booster versus control group. Changes in moderate-to-vigorous PA (p-interaction=0.13) and step count (p-interaction=0.18) did not differ between groups. CONCLUSION: The remote booster program effectively reduced ST and increased light PA in CAD patients. These findings highlight the potential to change physical (in)activity behaviour of patients beyond completion of traditional CR programs. TRIAL REGISTRATION: NCT06038188 (Clinical Trials.gov).