1. The total incidence of conduction disturbance was 6.50%, the atrioventricular block 3.14% and the intraventricular block was 3.36% of total 6,616 cases of E.C.G. reviewed. Among of these, the first degree atrioventricular block was 3.02% which was the most common occurred one, the incomplete right bundle branch block was 2.25% and the complete right bundle branch block was 0.57%.

2. The ratio of male to female was 1.6:1 for the first degree atrioventricular block, and 1.6:1 for the incomplete right bundle branch block, 2.5:1 for the complete atrioventricular block, 2:1 for the left bundle branch block, and 1.7:1 for the complete right bundle branch block. The first degree atrioventricular block was seen most frequently in the fifth and sixth decade of age group, and the third degree block was over 40 years. The incomplete right bundle branch block in order was forth decade, third decade and fifth decade. The complete right bundle branch block and left posterior hemiblock were common in the sixth decade. The left bundle block and the posterior hemiblock were common in fifty years of age group.

3. The cardinal underlying diseases of the first degree atrioventricular block among cardiac diseases group in order of frequency were: hypertensive heart disease (25.0%) arteriosclerotic heart disease (8.0%) and rheumatic valvular heart disease (5.0%). The most common etiology of those non-cardiac disease group was neuropsychiatry disorder (11.5%) and the next was infection (11.0%).

4. All of the complete atrioventricular block were associated with the cardiac disease, that is, 57.0% with arteriosclerotic heart disease, 28.5% with pericarditis and 14.3% with hypertensive heart disease, respectively.

5. The cardinal underlying disease of the incomplete right bundle branch block in order of frequency were: hypertensive heart disease (10.7%), arteriosclerotic heart disease (8.1%) among the cardiac disease group, and infections (15.4%) among the non-cardiac disease group. The incidence of healthy persons was 14.1%.

6. Those of complete right bundle branch block in order of frequency were: arteriosclerotic heart disease (13.2%), and hypertensive heart disease (10.1%) among the cardiac disease group, and infection(13.2%) and neurosis (10.1%), respectively among the non-cardiac disease group.

7. The major etiologies of the left bundle branch block was hypertensive heart disease and arteriosclerotic heart disease (33.3% each), and that of left posterior hemiblock was showed arteriosolerotic heart disease and cor-pulmonale. The most common etiological disease of the left anterior hemiblock was hypertensive heart disease in cardiac disease group, and infection and gatrointestinal disease in non-cariac disease group.

8. The abnormal electrocardiographic findings with the first degree atrioventricular block were left ventricular hypertrophy (24.8%), sinus tachycardia (11.0) and sinus bradycardia (5.8%). Those with the complete atrioventricular block were right ventricular hypertrophy (15.8%) and left bundle branch block (15.8%). In complete right bundle branch block, the majority (52.5%) showed single sign without other abnormality on E.C.G. In the left bundle branch block, there were 18.9% of left ventricular hypertrophy and 15.7% of first degree atrioventricular block. In the left anterior hemiblock, there were 28.5% of right bundle branch block, and 19.0% of right ventricular hypertrophy. In the left posterior hemiblock, there were 40.0% of atrial fibrillation and 20.0% of left atrial hypertrophy.