To assess the prevalence of obesity and investigate any changes in body mass index in children with CHD compared to age-matched healthy controls, in Southwestern Ontario.

The body mass index z-scores of 1259 children (aged 2–18) with CHD were compared with 2037 healthy controls. The body mass index z-scores of children who presented to our paediatric cardiology outpatient clinic from 2018 to 2021 were compared with previously collected data from 2008 to 2010. A longitudinal analysis of patients with data in both cohorts was also completed.

In total, 21.4% of patients with CHD and 26.6% of healthy controls were found to be overweight or obese (p < 0.001). The 2018–2021 cohort of CHD patients and controls had significantly higher body mass index z-scores compared to the 2008–2010 cohort (p < 0.001). Longitudinal analysis showed that body mass index z-scores significantly increased over time for CHD patients with data in both cohorts (2018–2021: M = 0.59, SD = 1.26; 2008–2010: M = −0.04, SD = 1.05; p < 0.001).

The prevalence of obesity in all children, irrespective of CHD, is rising. The coexistence of obesity and CHD may pose additional cardiovascular risks and complications.