The detrimental impact of extreme heat exposure on the health and well-being of children is widely acknowledged. The direct and indirect effects of climate change have led to an increased risk of certain cardiovascular events which may be particularly harmful to children who are born with, or develop, heart disease. To highlight the worrying paucity of investigative research aimed at differentiating how higher ambient temperatures further tax an already compromised cardiovascular system in children.  This commentary describes basic thermoregulatory concepts relevant to the healthy pediatric population and summarizes common heart diseases observed in this population. We describe how heat stress and exercise are important factors clinicians should more readily consider when treating children with heart disease. Countermeasures to physical inactivity are suggested for children, parents, clinicians, and policymakers to consider.  As sudden, excessive heat exposures continue to impact our rapidly warming world, vulnerable populations like children with underlying heart conditions are at greater heat health risk, especially when coupled with the negative physical activity and fitness trends observed worldwide.