The aim of this study was to determine factors associated with physical fitness (PF) in children who underwent surgery for congenital heart disease (CHD). Sixty-six children (7–14 years) who underwent surgery for ventricular septal defect (n = 19), transposition of great arteries (n = 22), coarctation of aorta (n = 10), and tetralogy of Fallot (n = 15) were included. All children performed PF tests: cardiorespiratory fitness, upper- and lower-limb muscle strength, speed, balance, and flexibility. Cardiac evaluation was done via echocardiography and cardiopulmonary exercise test. Factors related to child’s characteristics, child’s lifestyle, physical activity motivators/barriers, and parental factors were assessed. Linear regression analyses were conducted. The results showed no significant differences in physical activity (PA) level by CHD type. Boys had better cardiorespiratory fitness (difference = 1.86 ml/kg/min [0.51;3.22]) and were more physically active (difference = 19.40 min/day [8.14;30.66]), while girls had better flexibility (difference = − 3.60 cm [− 7.07;− 0.14]). Physical activity motivators showed an association with four out of six PF components: cardiorespiratory fitness, coefficient = 0.063 [0.01;0.11]; upper-limb muscle strength, coefficient = 0.076 [0.01;0.14]; lower-limb muscle strength, coefficient = 0.598 [0.07;1.13]; and speed, coefficient = 0.03 [0.01;0.05]. Age, sex, and motivators together reached a maximum adjusted R2 = 0.707 for upper-limb strength. Adding other possible determinants did not significantly increase the explained variance. Apart from age and sex as non-modifiable determinants, the main target which might improve fitness would be the introduction of an intervention which increases the motivation to be active.
