Introduction:Aortic dilation and dissection are life-threatening traits in Marfan syndrome (MFS). Clinical emphasis is often on what exercises to avoid to minimize risk of aortic dissection, rather than promoting regular exercise. Furthermore, MFS patients often lead sedentary lives due to self-imposed limitations. We have shown in an MFS mouse model that mild aerobic exercise can improve aortic wall characteristics and reduce stiffness leading to slower rates of aortic dilation.Hypothesis:We hypothesized that regular mild aerobic exercise can decrease aortic stiffness in pediatric MFS patients.Methods:We enrolled MFS patients aged 8-19 years old followed in our center to participate in a 6-month exercise intervention, excluding those with ventricular dysfunction or prior history of aortic surgery. We instructed patients to take 10,000 steps a day, tracked by an activity tracker. We checked in with patients weekly via phone call or text-messaging. At baseline and 6 months, aortic dimensions, arterial stiffness, endothelial function, and physical activity indices were obtained. Time spent in sedentary or vigorous activity was measured by accelerometry.Results:Nineteen patients (14.5?3.3 years old, 11 males) have been enrolled. Table 1 summarizes baseline data and initial results. Nine patients completed the intervention and 10 are currently participating. Three out of the 9 patients took at least 10,000 steps/day during the intervention. The other 6 patients increased their daily steps by 10% from 1stto 6thmonth. In these 9 patients, we observed a decrease in mean aortic root z-score by 9% and mean aortic stiffness indices by 30%.Conclusions:Our pilot baseline data confirm the rationale for the intervention showing that pediatric MFS patients have stiff aortas and lead sedentary lives. Our preliminary results are promising and support that this lifestyle intervention has great potential to improve arterial health in this vulnerable patient population.