The article is devoted to problem of syncope with cardiac arrhythmias in children. In pediatric patients, arrhythmogenic syncope represent the greatest threat to life and health. Arrhythmogenic syncope may be associated with weakness of sinus node, impaired atrioventricular conduction, paroxysmal tachycardia, syndrome of Wolff - Parkinson - White, long QT syndrome, Brugad's syndrome. Arrhythmogenic syncope are divided into 2 groups - bradiarrhythmical and tahiarrhythmical. The most common cause of arrhythmogenic syncope are ventricular tachyarrhythmia. Ventricular tachyarrhythmias occur in severe organic disease of the myocardium. Ventricular tachycardia with the transition to ventricular fibrillation is often the cause of sudden cardiac death. Syncope associated with bradycardia often occur in children with complete atrioventricular block, atrioventricular block of 2nd degree (2:1, 3:1 etc.). Weakness of sinus node causes syncope much less frequently. During sharp slowing of sinus rhythm the underlying atrium sinus nodes switch on which can provide a rate of 30-40 per minute. Syncope with weakness of sinus node occurs more often with bradycardia less than 30 per minute, and the presence of asystole periods of up to 2 seconds or more. The article presents clinical case of our own observation of a child with syncope. The cause of syncope was the syndrome of sinus node weakness with rhythm pauses to 9-14 seconds. It is not always possible to register syncope during daily Holter ECG monitoring. In this case, it is impossible to identify arrhythmogenic causes of syncope.