Inclusion Criteria:  Symptomatic sinus node dysfunction (dizziness, asthenia or syncope) clearly related to an abnormal electrocardiogram finding (sinus arrest, sinoatrial block, extreme bradycardia (<40 bpm) or chronotropic incompetence in the exercise test). Absence of structural cardiopathy  Exclusion Criteria:  Left ventricular ejection fraction <50% Severe valvular disease Any type of cardiomyopathy such as hypertrophic cardiomyopathy Previous ischemic heart disease QRS interval >130 ms Atrioventricular conduction disorder with a former indication of pacemaker implantation (atrioventricular block Mobitz II, advanced atrioventricular block, complete atrioventricular block) Lifetime expectance <12 months