Abstract Introduction Cardiopulmonary exercise testing (CPET) is an important diagnostic method to evaluate athletes and non-athletes, however we do not have widely accepted normal values for correct evaluation and interpretation in the young. Goals Our aim was to compare CPET parameters of young athletes and non-athletes and determine reference values. Methods Exercise tests were performed in young non-athletes, aged <18 years between 2011 to 2016 at Mayo Clinic. Athletes underwent detailed sports cardiology screening including CPET at Semmelweis University Heart and Vascular Center between 2016 and 2018. Individuals with cardiovascular disease were excluded. We created 2 subgroups in both sexes: 12–14 years (Group 1), 15–17 years (Group 2). Statistical analysis was performed using SAS with analysis of variance under the general linear model adjusting for age, body mass index and test effort based on peak respiratory exchange ratio (RER). Results A total of 212 athletes (92% male, 15.5±0.6ys) and 207 non-athletes (68% male, 15.0±0.7ys) were included in the analysis. In Group 1 boys, athletes have higher peak HR (200.0±9.2 vs 188.5±16.8 bpm, p<0.0001), HR reserve (117.1±14.5 vs 108.9±19.8 bpm p<0.05), VO2 max (53.7±6.6 vs 44.7±9.1 mL/kg/min p<0.0001), ventilation (VE) (120.3±25.0 vs 70.7±21.6 L/min p<0.0001) and RER (1.12±0.0 vs 1.07±0.08, p <.001) compared to controls. In Group 2 boys, there was no difference in peak HR and HR reserve, but athletes have higher VO2 max (57.2±4.7 vs 45.3±9.3 mL/kg/min, p<0.0001) and VE (150.7±23.7 vs 104.1±25.9 L/min, p<0.0001), similarly as Group 2 girls: VO2 max (46.3±3.6 vs 34.9±8.5 mL/kg/min p<0.0001), VE (118.7±12.5 vs 68.4±20.6 L/min, p<0.0001). In male athletes, peak HR (200.6±9.2 vs 196.5±7.4 bpm p<0.05) and HR recovery (34.2±9.8 vs 29.8±11.1 bpm p<0.05) decreases with age, while VO2 max (53.7±6.6 vs 57.2±4.7 mL/kg/min, p<0.001) and VE (120.3±24.9 vs 150.7±23.7 L/min, p<0.0001) increases. Lower cut-off values were determined in each group (Figure). Lower-cut off values Conclusion We created a unique Mayo-Semmelweis database of young athletes and non-athletes. As a result of intensive training, athletes show higher levels of CPET variables vs non-athletes. Our study provides CPET reference values in the pediatric age group, applying them could contribute to correct evaluation and interpretation of CPET, increasing its diagnostic potential.