marked sinus arrhythmia

My son a 10 year old, boy was diagnosed with sinus rhythm with marked sinus arrhythmia / otherwise normal ECG ( as the interpretation ECG readings). Is this a heart disease ? Is it curable ? Then what could be the best medical treatment for it.

[Brooke_38]

Sinus arrhythmia is a normal finding in children and young adults and tends to diminish or disappear with age. Sinus arrhythmia is often somewhat more prominent with fluctuation in the respiratory cycle as heart rate accelerates with inspiration and slows with expiration. The alternating acceleration and deceleration of heart rate with respiration is mainly the result of fluctuations in vagal tone. Sinus arrhythmia may be aggravated by any factor that increases vagal tone.