A healthy person has a healthy heart with a delicate and complete cardiac conduction system. Under normal conditions, the heart beats from the sinus node, which means that the sinus node controls the beating of each of our hearts. Sinus rhythm is the dominant rhythm of the heartbeat, which is called sinus rhythm in medical science. The sinus rhythm enables the heart to beat around the clock and work in an orderly and rhythmic manner to deliver oxygen and energy needed for life, maintain blood circulation throughout the body, supply various nutrients needed by the organs, and expel waste from the body in the process of metabolism so that the organs can perform their respective functions, enabling people to survive and babies to grow up healthy. However, children are in the growth and development stage, the heart is smaller than adults, the heart beats out less blood each time, so the only way to meet the body’s need for oxygen and various nutrients is to speed up the number of heartbeats, so the younger the age, the faster the number of heartbeats per minute. Sinus tachycardia in children under normal quiet conditions means that the number of heartbeats per minute exceeds the normal sinus rhythm, for example, if the heart rate of an infant is more than 140 beats per minute; if the heart rate of a child aged 1-6 years is more than 120 beats per minute; if the heart rate of a child aged 6 years or older is more than 100 beats per minute, it can be considered as sinus tachycardia. The most reliable means of diagnosing sinus tachycardia is a physician’s auscultation and an electrocardiogram. Does sinus tachycardia in children necessarily mean heart disease? Sinus tachycardia is most common in children, and doctors often refer to it as sinus tachycardia. For example, sinus tachycardia can often occur in children when they are crying, running or jumping, or when they are nervous; in addition, sinus tachycardia can be caused when children take drugs such as atropine and caffeine. When the above situation disappears, the tachycardia often disappears on its own, so this sinus tachycardia is temporary, a normal physiological reaction tachycardia, rather than heart disease, and does not require treatment. If a child has persistent sinus tachycardia, especially during sleep, parents should be aware that this may indicate the presence of some kind of disease, such as heart disease, rheumatic fever, etc.; sinus tachycardia can also be the first sign of heart failure. In addition, sinus tachycardia can also be manifested by other systemic diseases, such as hyperthyroidism, anemia, and chronic infectious diseases caused by various reasons, among which tonsillitis and pharyngitis are the most common. Therefore, parents should take their children to the hospital promptly when they find tachycardia, that is, sinus tachycardia, and ask the doctor to identify the cause.