To evaluate the relationship between aging and electrocardiographic abnormalities and arrhythmias, conventional surface 12 leads ECG findings were analyzed. The study group consisted of a total of 3,174 cases (1,778 men and 1,396 women, 17-87 years) without apparent organic heart diseases. The proportion of normal ECG progressively decreased with advancing age; it reached to the minimum of 20.0% in male and 22.7% in female after the age of 75. Frequency of supraventricular and ventricular premature complexes increased with advancing age as well as atrial fibrillation, left and right bundle branch block and left anterior hemiblock. Sinus bradycardia (less than 50/min) and the WPW syndrome did not follow this general trend but the former increased with advancing age after 55. Second and third-degree AV blocks were very rare in this study population. Right bundle branch block with left anterior hemiblock was not observed before age of 35, which may be regarded as a possible consequence of advanced age. Supraventricular and ventricular premature beats, and atrial fibrillation were more frequent in men than in women, but only in the older age stratum. Intraventricular conduction disorders were generally more common in men than in women. However, left bundle branch block was more frequently observed in female than in male in the older age stratum. The prolongation of QTc by oral IA antiarrhythmic drugs was observed after the age of 65. Thus, it was confirmed that aging might be important factor in abnormal findings and appearance of arrhythmias in conventional surface 12 lead ECGs.