Parents who bring their children to the doctor often complain of “fast heartbeat”, “tachycardia”, “arrhythmia”, “palpitations “. The parents’ questions are: Are these illnesses? Is it serious? Do they need treatment? In fact, the same complaints have very different conditions. Some may be normal, such as sinus arrhythmia; while others need active treatment, otherwise they may lead to cardiac insufficiency or even life-threatening. First of all, we need to determine whether the child’s symptoms or examination are normal or arrhythmia, which can be understood by touch or auscultation of the precordial area to understand the change of heart rate, so as to grasp the first-hand material. The diagnosis is further clarified by body surface ECG and 24-hour ambulatory ECG examination. In clinical practice, parents of children and even some doctors may encounter the following misconceptions: (1) The diagnosis of “bradycardia” or “tachycardia” is based on only one auscultation or ECG. Parents often consult with a simple complaint: “My child is tachycardic”. When asked how fast the heart is beating, the answer is often “more than a hundred”. The diagnosis process is not so simple. Unlike adults, the younger a child is, the faster his or her heart beats, so the normal range of heart rate varies by age group. Secondly, there are many factors that affect the heart rate, and the heart rate fluctuates within a certain range. It is difficult to simply judge whether the same heart rate is normal or abnormal at the same age. Usually, we need to evaluate the heart rate in combination with whether the ECG pattern is normal or not, and especially important is the 24-hour ambulatory ECG examination to understand the range of heart rate fluctuation throughout the day. (2) Auscultation of “arrhythmia”. Sometimes parents are often nervous when they are told they have an arrhythmia during a physical examination or at a doctor’s appointment. Arrhythmia is a general term that encompasses more specific diagnoses, such as sinus arrhythmia, which may be related to breathing and is a normal physiological phenomenon. Other common ones are premature beats and atrioventricular block, which are sometimes more difficult to identify by auscultation alone and require further electrocardiographic examination. (3) Paroxysmal tachycardia with normal auscultation or electrocardiogram during the interval of onset. For paroxysmal episodes of tachycardia, such as the common paroxysmal supraventricular tachycardia, the heart rate is very fast, up to 160-300 beats/min, and the duration varies, and some children may last only a few minutes, which is difficult to capture on the body ECG or even 24-hour ambulatory ECG. Parents of such children should not panic at the onset of the disease. Careful observation of the child’s performance and measurement of the heart rate at the onset of the disease can provide the doctor with reliable first-hand materials and a basis for diagnosis. Does the arrhythmia need to be treated? What method of treatment should be chosen? 1.Sinus tachycardia Sinus tachycardia is usually physiological and does not require treatment, except as a concomitant symptom of certain diseases, such as hyperthyroidism, myocarditis, beta-receptor hyperfunction, inappropriate sinus tachycardia, etc. 2.Paroxysmal supraventricular tachycardia This is the diagnosis of a group of diseases. It includes preexcitation syndrome, atrioventricular node folding tachycardia, atrial tachycardia, atrial flutter, and, rarely in the pediatric population, atrial fibrillation. In most cases, the physician can make the diagnosis by ECG. (1) Preexcitation syndrome: Also known as atrial fibrillation tachycardia, it is most common in pediatric supraventricular tachycardia (50-60%). It is due to an abnormal development of the fetal heart and the presence of a bypass with conduction function across the atrioventricular annulus, called an additional bypass. Due to the presence of this additional bypass, abnormal excitation conduction can occur in the heart, causing tachycardia. The heart rate can be as high as 200-300 beats/min during the tachycardia attack, and in severe cases, continuous attacks can lead to cardiac insufficiency or even sudden death. The application of radiofrequency ablation in the treatment of pediatric preexcitation syndrome has become the first-line treatment of choice for physicians because of its mature method and proven efficacy, with an overall success rate of >96%. (2) Atrioventricular node regurgitation tachycardia: The incidence of atrioventricular node regurgitation tachycardia in pediatric patients is second only to that of preexcitation syndrome, accounting for about 16-20% of pediatric supraventricular tachycardia. It is due to the abnormal formation of two pathways in the atrioventricular node, a very important part of the cardiac conduction tissue, during fetal development, called the atrioventricular node double pathway. Due to the presence of the atrioventricular node double pathway, abnormal excitation conduction can occur in the heart, causing tachycardia. The clinical presentation is the same as that of the pre-excitation syndrome. The success rate of radiofrequency ablation for atrioventricular node tachycardia in children is 95.7%-97%, and the recurrence rate is slightly higher than that of preexcitation syndrome. (3) Atrial tachycardia (atrial tachycardia): pediatric atrial tachycardia is not uncommon, accounting for about 6% to 10% of supraventricular tachycardia, and can develop from the neonatal period or even during fetal life to older children. In mild cases, atrial tachycardia can occur in short bursts, but in severe cases, it can last for several years without interruption, causing heart enlargement and cardiac insufficiency. Anti-arrhythmic drugs are preferred for pediatric atrial tachycardia. Some children can be cured by antiarrhythmic drug treatment, but about 40% of children with atrial tachycardia are difficult to treat, and various antiarrhythmic drug treatments are ineffective, so radiofrequency ablation can be considered. The success rate of radiofrequency ablation for pediatric atrial tachycardia is about 60-90%, and the success rate is related to the location of the origin of atrial tachycardia. We have also met some newborns and even fetuses with severe atrial arrhythmias, the cause of which is not clear, but after early, aggressive and sufficient courses of antiarrhythmic drug treatment, they have all returned to normal. Premature ventricular contractions are very common arrhythmias in childhood and most of them have a good prognosis. Most children with occasional premature beats have no obvious clinical symptoms and are often detected during physical examination or electrocardiogram. Although these premature beats are benign, their prolonged presence limits the child’s physical activity and seriously affects the child’s quality of life and is extremely disturbing to the parents. There is no specific treatment for premature ventricular contractions and most of them do not require interventional therapy. Prolonged and frequent premature beats, such as >10,000 beats/24hr or >20%, may lead to left ventricular enlargement and cardiac insufficiency, which may be treated with antiarrhythmic drugs or radiofrequency ablation. Radiofrequent monogenic ventricular premature beats originating from the right ventricular outflow tract without organic heart disease are safe and effective with a success rate of 81% to 83% with radiofrequency ablation.