Normally the heart rate (HR) rises with the exercise to increase the amount of blood across the lungs and thus get higher oxygen to the tissues that will require more energy. The maximum heart HR is 220 minus age, so children have a higher maximum HR than adults, as example a 5-year-old can reach at 215 bpm (220-5 yr = 215 bpm) when running at high intensity.
If the child shows chest pain or chest discomfort when running could be signs of alarm. Your pediatrician will assess the need for an appointment by a specialized cardiologist.
Some situations make the heart go faster, for example anemia (less haemoglobin, so the heart compensates by increasing the heart rate to increase the oxygen transportation) or hormonal alterations, among them hyperthyroidism (the elevation of thyroids increases the heart rate), and conversely, in hypothyroidism the heart goes slower.
In case of palpitations the pediatrician should be consulted and blood analysis should be performed to rule out extracardiac abnormalities.
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