Abstract Background Coronary atheromatous plaque geometry, expressed as plaque burden (PB) or total atheroma volume (TAV) are both strongly related to the risk of acute and recurrent coronary events and outcomes in coronary artery disease (CAD). Exercise training is a cornerstone in the primary and secondary prevention of atherosclerotic complications, but the knowledge of the effect from exercise on coronary atheromatous plaques is sparse. Purpose We assessed the effect of six months supervised high intensity interval training (HIIT) on coronary plaque geometry using intravascular ultrasound in patients with stable CAD following percutaneous coronary intervention (PCI). Methods Sixty patients were randomized to two sessions weekly of supervised HIIT at 85–95% of peak heart rate (n=30) or to follow contemporary preventive guidelines (control group, n=30). The primary endpoint was change in PB and TAV normalized for segment length (TAVnorm) at six-month follow-up. All included patients were on stable lipid lowering therapy at least six weeks prior to inclusion with no further adjustments throughout the study. Results When comparing matched coronary segments at baseline and follow-up, there was a 1.4 percent points larger reduction in average PB (95% CI: 2.7 to 0.1, p=0.036) in the HIIT group compared to the control group. TAVnorm was reduced by 9 mm3 (95% CI: 14.7 to 3.4, p=0.002) after HIIT, with a between group difference of 12 mm3 (95% CI: 19.9 to 4.2, p=0.003). VO2peak improved more in the HIIT group with a difference in delta VO2 peak between groups of 1.7 mL kg–1 min–1 (95% CI: 0.1 to 3.3, p=0.039). There was also a significant larger reduction in body mass index and waist circumference in the HIIT group compared to the control group (both, p=0.021). In both groups a modest, although significant increase was observed for both HDL-cholesterol and ApoA1, but no significant changes in the LDL, ApoB or HbA1c levels were found. Conclusions In patients with established CAD, a regression of PB and TAV was observed in patients undergoing six months of supervised HIIT compared with patients following contemporary preventive guidelines. Our study indicates that exercise increasing VO2 peak counteracts atherosclerotic coronary disease progression and reduces PB and TAV in coronary atheromatous plaques following PCI. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): This study was funded by the Liaison Committee for Central Norway Regional Health Authority, the Norwegian University of Science and Technology (NTNU), and the Research Fund at St. Olavs University Hospital