Sinus tachycardia with arrhythmia is diagnosed on the patient’s ECG as sinus rhythm with a heart rate of 100 beats per minute or more, accompanied by sinus arrhythmia, and there are many people who experience this symptom. An increased heart rate due to stress, fever or after activity may be accompanied by arrhythmia, and there is no need for special concern; most of them are normal after the heart rate is brought under control. Many infants and children with heart rates above 120 beats per minute may also have such ECG reports, which are of no particular significance. If there is a fever caused by a cold, it is also necessary to exclude the possibility of myocarditis, because myocarditis itself is prone to this ECG diagnosis.