Exercise capacity significantly affects Pompe patients' clinical picture and quality of life [5]. However, data on the effects of ERT on physiological variables related to exercise capacity is scarce. Cardiopulmonary exercise testing (CPET) is a well-known procedure to assess exercise capacity in adults and children in healthy and chronic conditions. Little is known regarding exercise capacity in the pediatric Pompe population. Our aim was to evaluate the acute effect of ERT on exercise capacity and different physiological variables in pediatric Pompe patients.