Dizziness, black spell, syncope, short of breathness and heart failure due to cardiac arrest or severe bradycardia are often observed in patients with atrioventricular(AV) block or sick sinus syndrome(SSS). Not only danger of cardiac sudden death but also accidents such as bone fractures, traffic accidents are great problems especially in elderly patients. These symptoms are improved by pacemaker implantation. Atrial fibrillation is often observed in patients with brady-arrhythmias, especially in patients with sick sinus syndrome. High incidence of cerebral embolisms is also great problems. Specificity of electrophysiological study for brady-arrhythmias are high but sensitivity is not enough. Diagnosis of AV block and sick sinus syndrome can be determined by medical histories, conventional ECG and Holter ECG.