Engagement in exercise-based cardiac rehabilitation following cardiac procedures reduces the risk of secondary coronary artery disease (CAD) events. Interval training can be a time-efficient and effective alternative to traditional moderate-intensity exercise in cardiac rehabilitation programming, and an accessible way to deliver interval training is through stair climbing. PURPOSE: To assess the feasibility and effectiveness of high-intensity interval training intervention, using stair climbing as the modality, in standard cardiac rehabilitation care. METHODS: Twenty participants with CAD (61±7 y, 18M/2W) were randomly assigned to one of two exercise programs: traditional moderate-intensity exercise (TRAD) or high-intensity interval stair climbing (STAIR). VO₂peak was assessed at baseline, one month and three months after exercise initiation. Exercise was completed two times/week for one month under clinical supervision, and three times/week for two months unsupervised. Each participant completed sessions of either an accumulation of 45 min at 80 %HR_peak (TRAD) or 3 bouts of 6 flights of 12 stairs at a self-selected vigorous intensity (~90s/bout) separated by recovery periods of walking (~90s) (STAIR). RESULTS: Eighteen participants (90%) completed the intervention without any adverse events. Following one month of supervised exercise, the STAIR versus TRAD group achieved a higher peak HR 131±9 vs.111±13bpm (p=0.002, means±SD), and exercise intensity 106±11 vs.89±1%HR_peak, across a shorter time 3.1±0.8 vs. 36.7±5.5 min (p<0.001). Peak VO₂ increased in both TRAD and STAIR, (23±3 to 25±4 and 21±5 to 24±6 mL/kg/min) respectively (p=0.03). Additional unsupervised training (2mo), the STAIR group achieved a higher peak HR, 126±13 vs.111±9 bpm (p=0.018) and less time at prescribed intensity 6.5±3.9 vs. 24.2±17 min (p=0.012), when compared to the TRAD group. There was no difference in exercise intensity 96±8 vs. 87±8 %HR_peak (p=0.055) or adherence 3.0±3.2 vs. 3.2±2.2 (p=0.70) exercise sessions/week, between the STAIR and TRAD groups. CONCLUSIONS: High-intensity interval training using stair climbing as the modality, is safe and effective within cardiac rehabilitation programming.