Sinus tachycardia refers to an increase in heart rate that is physiologically appropriate for the given condition or activity level. In children, the normal heart rate varies with age, so what is considered tachycardia can also vary. For instance, a heart rate above 160 beats per minute (bpm) may be considered tachycardic for an infant, whereas for older children, the threshold might be 100-120 bpm.
