Sick sinus syndrome (SSS) describes an arrhythmia phenotype attributed to dysfunction of sinus node. It is frequently associated with heart disease and occurs in the elderly, much rarer in children, and it also may occur in the foetus. The typical arrhythmias for sinus node disease in standard or Holter electrocardiogram (ECG) is the basis of diagnosis. Paediatric patients may be asymptomatic, may have impaired exercise tolerance, syncope, or fainting. Sinus node dysfunction in a young person without associated heart disease is suspected to be congenital and needs a deepening of family history. In the article is presented siblings with sinus node disease. In both of the children with normal heart, on ECG sinus bradycardia with supraventricular wandering pacemaker dominates. Up to now, none of them had presented any symptom. They do not require a permanent cardiac pacing. Because of the potential progression of the disease they need to be under the cardiologic observation. The children’s father suffered from bradycardia, in their grandfather a peacemaker was implanted when he was young. The mother and brother of those children have normal cardiac rhythm. The occurrence of sinus node dysfunction in children, their father and their grandfather suggests a familial sick sinus syndrome.